Custom extensions and bulk extension module

I would like to import a bulk of custom extensions into FreePBX, all of which should must have an individual custom dial string that goes like that: SIP/“trunkname”/“custom extension”. Is that possible using the csv file?

When these extension are dialed I want them to be sent on my internal trunk to my legacy PBX.

The reason why I don’t just have an outbound route for these numbers is, that I want them to appear in FOP2.

Yes it works. Use the bulk extension template or export existing extensions into csv to see how that looks.