How to add frequencies?

Good day,

nowadays almost every dxpedition uses "non-standard" frequencies for their operation. How can I add these frequencies to the list?

Or let me put the question in another way:
How can I prevent JTDX to return to standard frequencies after changing the callsign to the club call from my personalsign call (or vice versa)?
It is quite annoying having always to retune to the non-standard frequency.

Thanks and 73 de Adi DL1EZ