I would like to change the default shell in each terminal emulator separately. To clarify, I want Xterm to use TCSH, pterm to use pysh, gnome-terminal to use BASH, etc. Is this possible? If so, how can this be accomplished.
Each terminal emulator has its custom way to select which shell to run:
So you need to discover, by reading the manual, how (and if) each terminal emulator can be configured. There is no common way :-(
If you need only a simple way to choose which shell to run, I strongly suggest you to choose a terminal emulator that supports profiles (like gnome-terminal) and to create a different profile for each shell type. This way you'll can launch a new tab or window running the needed shell by the gnome-terminal internal menu (and, as bonus, choose a different text color for each shell).
As a quick and contained solution, you could make a wrapper script.
Just use it as such:
It's generally preferable to configure each terminal emulator individually though.