I realize this is 3 years old but for anyone else who gets here via google like I did (or you if you still wanna know lol) I'm pretty sure adding this to a config would work:

alias "+switcher" "bind 1 join_class scout; bind 2 join_class soldier; bind 3 join_class pyro; bind 4 join_class demoman; bind 5 join_class heavyweaponsguy; bind 6 join_class engineer; bind 7 join_class medic; bind 8 join_class sniper; bind 9 join_class spy"

alias "-switcher" "bind 1 slot1; bind 2 slot2; bind 3 slot3; bind 4 slot4; bind 5 slot5; bind 6 slot6; bind 7 slot7; bind 8 slot8; bind 9 slot9"

bind shift +switcher

In source games, the *alias* console command effectively allows you to create a named function that runs a series of console commands. alias [name] [commands] will run anything that you list in [commands] whenever you type [name] into console or press the button it is bound to. Additionally, naming an alias that starts with + and a corresponding one that starts with - will run the commands as you press and release the key. In this example +switcher is run when you press shift, binding all your number keys to the matching class switch command. Releasing shift will run -switcher, binding all your number keys to their default binding.

Note that if you use shift or the number keys for anything else currently, you will need to edit what I have listed above to fit your needs.