I just flew in on Sunday. It was funny to see that although we were not permitted to carry water, juice, lotion etc. Folks that bought liquor at the duty free were permitted to carry it on board and down to Belize.
So, you can most likely purchase your tequila at duty free (so called secure area)- don't open the sealed package and you can pass it through customs in Belize. If for some reason the customs guys confiscate it - you will have contributed to their hangovers the next day!!
By the way, my kids came in from the UK on Saturday - whole other story. The customs over there tipped out peoples purses, picked out their passports and cash, placed those items into a clear plastic bag and dumped all of the other items - cell phones, ipods, laptops - all in the trash.
Keep up to date with the regulations - and you won't be disappointed.
Have a fantastic trip to Belize.
Maybe we can covert you into a rum drinker!