move from one extension to another

[ButterOil]

Is it possible to move from one extension to another directly? without returning to Matras

[Elendil / Redshift]

Check the Sea Captains Verra (Matras) and Hanty (Mithria) in the base world (Freymore) with the editor.

You'll see that they have a special line "addobjecttolist("exppack3","exppack3");" (or with "exppack1") in their code to build their list of travel destinations. This line adds all installed expansions which are either high level ("exppack3") or low level ("exppack1") to their travel list. Then you can use the "player.movebyship(target,
"The ship takes you there.");" line to move to the selected destination. (With "target=getobjectlistresult();")

This is the only way. You must present the whole list to the player and travel to the destination they selected. There is no way to travel to a specific expansion directly.