It's hard to tell based on those clips how your tone would be affected because that clip has quite a lot going on but it sounds like you are getting very good tone from your amp already. I would say that the mod would take you more into a gainier more tightly focused sound. Or at least the ability to do so. You could probably get the same tones your getting now but you would have to set knobs a little differently. Plus you could get better tones at much lower volumes with the effects loop mod in place. If you like your tone now it might be best to leave it alone. Why mess with a good thing?
Mike B. at Mesa does this mod. I wouldn't recommend having anyone else do it. I still say the difference this mod makes it night and day, especially if you want to use your IIB for hard rock or metal. I A/B'd the modded IIB against my C+ and the C+ had a slightly more vocal lead sound but in every other regard the IIB could match it every step.