Submitted by: @pavel-zotov

On empty database (Firebird version: WI-T3.0.0.31807, tested on SS and SC) do:

TEST-1.
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---------------- start of script `test1.sql` ---------------
set term ^;
create procedure sp_dummy(a_id int) returns(o_txt varchar(20)) as
begin
o_txt = 'get id='||a_id;
suspend;
end
^
set term ;^
commit;

set count on; set echo on;
update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;

rollback;

update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;

rollback;
---------------- end of script `test1.sql` ---------------

Run: isql.exe localhost/port:<path>\<file> -i test1.sql 1>result1.log 2>&1

Result-1:
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update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1

rollback;

update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1

rollback;

(So, each DML really can update at least one row - we can see it in affected records; and NO errors occured).

TEST-2
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Recreate again new database and apply following:

---------------- start of script `test2.sql` ---------------
set term ^;
create procedure sp_dummy(a_id int) returns(o_txt varchar(20)) as
begin
o_txt = 'get id='||a_id;
suspend;
end
^
set term ;^
commit;

set count on; set echo on;
update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;
rollback;
---------------- start of script `test2.sql` ---------------

Run: isql.exe localhost/port:<path>\<file> -i test2.sql 1>result2.log 2>&1

Result-2:
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update RDB$PROCEDURES t set t.RDB$PROCEDURE_SOURCE = null where coalesce(rdb$system_flag,0)=0 rows 1;
Records affected: 1
rollback;
update RDB$PROCEDURES t set t.RDB$RUNTIME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PROCEDURES
After line 13 in file test2.sql
Records affected: 0
rollback;
update RDB$PROCEDURES t set t.RDB$ENGINE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PROCEDURES
After line 15 in file test2.sql
Records affected: 0
rollback;
update RDB$PROCEDURES t set t.RDB$ENTRYPOINT = null where coalesce(rdb$system_flag,0)=0 rows 1;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PROCEDURES
After line 17 in file test2.sql
Records affected: 0
rollback;
update RDB$PROCEDURES t set t.RDB$PACKAGE_NAME = null where coalesce(rdb$system_flag,0)=0 rows 1;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PROCEDURES
After line 19 in file test2.sql
Records affected: 0
rollback;
update RDB$PROCEDURES t set t.RDB$PRIVATE_FLAG = null where coalesce(rdb$system_flag,0)=0 rows 1;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PROCEDURES
After line 21 in file test2.sql
Records affected: 0
rollback;

How could 'rollback;' statements that are placed after each DML prohibit all subsequent updates except first one ?