Block H+ (3.5G) but not H (3G), possible? Is there any way to block only H+ (3.5G) and still have H (3G)? I use Android 4.2.1 CM10 Galaxy Nexus.

I want to do this because 3.5G signal in buildings is poor (1 bar), but 2G (which signal is good) is too slow.
No, you cannot block that, unfortunately! 

You can either switch to 2G (which saves battery) or continue with 3G. Cannot have it both ways! 

The telephony signal is deep within Android itself and no way of messing with that! Not alone that, Android picks up that radio signal strength from the heart of the Silicon On Chip (S-o-C) where the base-band radio firmware resides in and is off-limits and proprietary.