Problems if changing rulesets mid savegame?

[mark617]

1) I want to make the game more grindy. If I change the power setting (weapon damage) in items.rul and alien health in units.rul, is there any potential for problems doing so mid game (corruption to savegame etc.)?

2) Do the above changes take effect immediately (I assume so since the UFOPaedia changes immediately)?

Thank you very much 

[Meridian]

no corruption.
do the change during geoscape.