What I would suggest is that you set up a basic test forum, install EasyMod and use this to test out the mods before ever doing anything on your live forum. That way if things get pear-shaped then you can just wipe the test and restart.
However, an easier way is to read the mod, find out what files are involved and copy them to your hard disk. That way you can just copy them back if it goes bad. Mind you, undoing an SQL command may not be so easy!
As an example, I downloaded a "report post" mod from www.phpbb.com
. This failed miserably and when I posted about it the author came back to say it was an old mod and to use the new one - which he quoted. Both were registered as version 1.0.0 and both did not work. I am still waiting to hear why he did not update the mod version, post the new mod to the verification team and what he is going to do about the next failure.
I now have a version - yellow_card
- that works and is ready to port over to the live forum.