Is there a way to change phone's modem?

Hi guys,
I'm having a problem with my phone for a while already.
I have HTC One M8 of T-Mobile.
I'm currently living in Israel, and I bought it here locally from some private mobile store, back then I didn't really realized the difference
between International to all other like T-Mobile, AT&T and such.
After I moved to my current ISP, I'm having trouble with low reception in some places while other phones with my SIM card are working fine and getting good reception.
I understood it's happening because of the modem the T-Mobile are using, it's using other frequencies that aren't available here, only in US and such.

So, is there a way to flash or something a new modem? Or is it something that is hardware based?

Thanks in advance! :good: