If you're on 3.9.x, the default (Ubuntu) location is:
/home/hts/.hts/tvheadend/input/dvb/networks/<UUID>/muxes/<UUID>/config
... so OpenElec will be something like /storage/.hts/... or similar. The first UUID identifies the network; the second is then the mux.
Now, whether you can simply copy these elsewhere, I have no idea, as the UUIDs may not be portable. You'd have to try, I suspect - or maybe stop tvh, remove a mux config, restart it and see what happens, and then stop/replace/restart to see if it reappears.
I suppose the other angle would be to quickly define a few 'fake' or 'dummy' muxes, stop tvheadend, replace the fake mux configs with the ones from your old installation, and restart the service. That at least would bring over all the settings like frequency, bandwidth, encoding, etc. and isn't dependent on the UUIDs as those would be generated by the fake muxes.
Finally, auto-discovery typically works well if you give it time, so you only really have to add one good mux and the rest will normally follow.