To put my $.02 on your question, the easiest way to get your Bassman to
sound more like a BF is to bypass the cathode follower that drives the tone
stack.  You can do this by adding a DPDT switch.  Maker sure it's rated for
200V or better.  You have to switch both the input and the output to the
cathode follower.  All the connections you need are on the tube sockets, so
it's not that bad a mod on the RI's.  If this all sounds alien to you, find
a good tech.  If it's an original Bassman, I wouldn't do it and we need to
talk.

The mod I described does go a long way toward toning down the
tendency toward harsh treble response in the RI Bassman. That is 
obviously the key knock on these amps.

If you want a more modernistic thing, change the
preamp cathode bypass/resistor combination to
2.2K/0.68UF, put a 500pf cap in the tone stack in place
of the 250pf, change the output coupling caps from .1uf
to .022uf and add grid stoppers between 1.5K to 3.3K
(to taste, bigger value = darker) on the grids of the
outputs.
 
Of course if you do all of that, you might as well
change the screen resistors to 1K and set up the bias for
EL34's and change the output transformer too.
 
Or you could buy a Marshall. ;-)