I have a Bushmaster 556/223 with an adjustable  stock that I would like to put a reg. stock on.  My question is with the buffer tube being a commercial style tube can I replace it with a Mil-spec buffer tube and spring without having to do a lot of changes.  Never done this before, so before I make a move I wanted to make sure this could be done without problems.  Thanks in advance to all who reply.

By "regular" stock do you mean a fixed a2 rifle style stock? If that's the case you'll need a new buffer tube, spring and buffer. Best to just buy a complete stock kit that includes everything.
This kit shows everything that you need.  http://palmettostatearmory.com/a2-rifle-stock-kit.html
I think bushmaster may have used locktite on their buffer tubes at some point, so watch out for that, otherwise just get your castle nut backed off, unscrew the tube, watching out for the take down pin detent spring and the buffer retainer. Screw in the the rifle tube and put on the rifle stock with appropriate spacer and screw and install the rifle buffer and spring.
If you mean you want to install a mil spec telescoping stock, like m4 stock, then all you need is the mil spec tube and stock, all other parts are the same.

Sorry, yes I did mean for an A2 style stock that is Mil-Spec. Thank you for the information, it was very helpful and what I was wanting to know.