//Alias for left and right weapon hands
alias lefty "cl_righthand 0;"
alias righty "cl_righthand 1;"

//Attach the appropriate weapon hands to the weapon selection buttons
alias newknife "slot3; lefty;"
alias newnade "slot4; lefty;"
alias newc4 "slot5; righty;"
alias newpistol "slot2; righty;"
alias newprimary "slot1; righty;"

//Toggler for the new and old control sets on the weapon selection keys
alias controls newcontrols
alias newcontrols "bind 1 newprimary; bind 2 newpistol; bind 3 newknife; bind 4 newnade; bind 5 newc4; alias controls defaults;"
alias defaults "bind 1 slot1; bind 2 slot2; bind 3 slot3; bind 4 slot4; bind 5 slot5; alias controls newcontrols;"

//Bind a key of your choice to toggle this script on and off
bind - controls

This script will only work on the weapon selections keys (1 to 5). If you choose weapons by scrolling the mouse, or with the [ and ] keys, they are bound to invnext and invprev. This means you can go back or forwards at random and it can't be scripted to change weapon hands reliably.