some have DIY'd. You can find them if you search. From what I've read, it is a time consuming job. Parts are cheap, but labor is not. An indy quoted me $580.
I'm considering DIY, but from what I've read there is a risk to breaking the breather hose and the cover itself is very tricky to remove. Haven't seen a "best method" or trick to getting the cover off.
The DIY here: http://www.e90post.com/forums/showthread.php?t=697252
is for replacing eccentric shaft sensor but requires changing the vcg. The writer gives some tips for removing the breather hose and other steps related to vcg change.
If you have a plastic cover, you may not need to replace bolts, per suggestion in above post. If bolts have blue spots on them, they need to be replaced. Mine do not. The DIY above does not replace bolts.
Don't know about your question regarding replacing the plastic cover. I've wondered about the pcv mechanism, ie is there anything to inspect on the old cover to determine if replacement is warranted?