Yes on both accounts.
I put the 'cap' back over the recessed area after the drilling, and flared it out a bit so the exhaust can flow better. Also provides some potential deflection for an errant spark, not a huge issue when up a tree, but...
Check the 'MS150 has arrived' thread on the chainsaw forum, our saw mod guru Mastermind tore one down and rebuilt it...the best basic mod without going nuts is the muffler mod.