Based on my experience and presuming an equivalent bug logger, its going to be pretty hard to ruin something and not know how to repair it, plus if you get source control set up you can revert changes if somehow you can't fix them.
You are working on a pretty high level in Glest engines compared to something like writing your own graphics or physics engine where you are down in the nitty gritty.
If you follow the code conventions and stick mainly to gameplay, even if its complex like effects and emanations, you shouldn't run into any real trouble.
