Not sure why you would ever want lower tick rate, CS:GO players complain about official servers having 64 tick, and often go to private servers so they can get 128 tick (which is noticeably more responsive for hit registration in those tight, panicked moments).
However, the client should be able to set his own values for cl_rate, cl_updaterade, and cl_cmdrate to better suit his own internet speeds, as long as the server isn't forcing certain minimum values for all clients (or TF2 itself forcing it, CS:GO forces them across the board pretty much).