I don't know how long it will be before a phpbb3 compatible easymod version will be released (and I haven't taken a look at the easymod code to see how easy it will be to adapt easymod to phpbb3). But in the interim, here's a workaround that I haven't tried but that should work fine:
Assume you have a phpbb3 test board working correctly under a folder called phpbb3 and a live or test phpbb2 board (with easymod installed) working correctly under a folder called phpbb2, and you have a phpbb3 mod script you want to install in your phpbb3 test board. Try this:
- move the phpbb3 folder so that it is a subfolder under your phpbb2 folder
- go through the phpbb3 mod script and prepend all the file references in the OPEN commands and the COPY commands with 'phpbb3/'
- install the mod the regular way using easymod (but don't let easymod do the db changes...you should run those separately)
- move the phpbb3 folder back where it used to be
- run any database changes the mod has you make via phpmyadmin or whatever other db gui you use
That's all there is to it. Like I said, I haven't tried this but it should work fine.