Yes, of course. the I9100 & I9100T (I also have an I9100T) are exactly the same except for a very slight difference in radio output, achieved by firmware - the modem.
If you flash an I9100 stock rom, it will include an I9100 modem which might
(not always though) mess with your connectivity, and as I hinted at in my PP, in my experience, using modems which have been bundled with stock roms released by carriers which sold the I9100T tends to result in the best connectivity. You can check these by searching the I9100T firmwares on Samfirmware, which lists the baseband (modem), and you can then find/download whatever modem in question here
However, if after flashing an I9100 stock rom your connectivity is OK, no need to change the modem. Only change the modem if your connectivity isn't great. Custom roms don't include modems, so flashing a custom rom won't change your current modem.