Mandar,
Global variable feature was introduced part of 9.x release, and it was not in 8.x.
When you talk about upgrade, the code as such from 8.x will be migrated to 9.x, and it will work the same as it was before…
Now, you want to use a new feature that is introduced part of 9.x ie., Global variable substitution… This requires some change which needs to be done in the code… Yes, as you did, you have to edit each and every flow service if you want to set a value for a variable, and tick the check box…
Doing it using script, or changing directly flow.xml is not recommended & they are highly prone to errors. Its a change that is expected in a service, and treat that as a code change. This has nothing to do with migration.
regards
Senthil
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