So could you put 355 blades on a B model and get an uprated MTOW like a BA?
To do that it would have to be a BA. You can do this mod via SB 01-35.
Then if you have loads of cash you can go from BA to B2 with SB 01-50.
If the aircraft is eligible of course with respect to modification and previous SB status. It may not be economic if you have an old MR Mast etc. etc. etc...........
You may be able to do the B to BA in the field but I think the BA to B2 may only be authorised for EC.
"Call your friendly EC dealer/distributor"
here 