Can you save the outbond and/or inbound travel also for after your first trip(s)?

Thank you!

Say that i did already use my out- and inbond tickets on my Global Pass, and that i took the train home to Brussels for a short break between travels and want to leave again a few days later from Brussel (home) to Paris by TGV. Is this possible, and will the rail planner app allow me to book the ride and pay for the part to the border only right away?

Or how would i have tot do this if my in- and outbond tickets are used already and i want to bord in Brussels. Thank you again!

As TGV is a global price train, you likely won’t be able to purchase a ticket to the border only. You’d have to book a ticket to the first stop in France + a reservation for your interrail ticket from there to Paris (if there is a stop in between).
Better to use an IC service to Lille and take a TGV from there (or actually you can save the money and go by TER trains to Paris, although that takes of course way longer).

Thanks a lot, its clearing out.

To go to NL its local=much cheaper NMBS tariff till Roosendaal en Maastricht (en also Aachen=Aix la Chapelle in DE), but not to Noorderkempen-Breda. To Breda you can-at least 7 days advance, but without train-binding, buy much better priced advance tickets.

To go to LUX go via Athus then free CFL, via Arlon direct is rather cumbersome, ;pay till Arlon+book onward from there online.

Note that NMBS charges much, much higher fares for tickets till borderpoints and as they can only be issued in travelcentres there is also the 7,50 extra fee.

Its indeed much wiser to keep the trips OUT+IN for direct TGV  trips, as otherwise its really a very expensive method. For to go UK use €* only to/fro Lille.

I have a related question. 
 

If I have used my inbound/outbound home ticket, France, and then I’m going to London from Brussels Midi, but I have to pass from France (country of residence) will the app allow me to pass.

If you live in France (your profile says Pakistan) then passing through France with the Eurostar will use one of your inbound/outbound journeys.

@MartinM The Thalys Brussels - Paris will indeed require one or more passes so that the whole route is covered with valid passes. The TGVs from Brussels to France however also have fares for people with a valid pass only for Belgium or France.