I really did not understand 100% your question
If you want to have the EPG on for example HDD
instead of USB, then simply change a path
But you can not change the path that is unknown in the system of EPG
It is also not possible in CrossEPG
And there you can only choose path which is known within the plugin
It may be possible by changing the coding and configuration
but I do not see the sense of it.
But you can experiment with changing the path in
settings file /etc/enigma2
(config.misc.epgcache_filename=/media/usb/epg.dat)
But if it works ?? I have not tested