First winter with new bike...
 

The bike has 26x2.0 tires, come January I may want to put studded ones on it but to educate the uneducated do I go 26X1.95 or 26X2.1 as these seem to be the sizes that are made near to what is on there now. The rims are Matrix 550 rims.

There is flexibility in what the rims support; you could go either way as those widths are extremely close to your stock tires. If you go too far in a particular direction (like less than 1.5"), I'd check with the rim manufacturer.

The other concern (for me at least) is when switching between tires (like studded and nonstudded) I'd like to reuse the same inner tube if possible. In other words having one set of 2" tires and another set of 1.5" tires would probably require different sets of tubes.

Thanks!!, that's what I was hoping..on to shopping for some Nokian's :)