Could you disassemble it and put a spacer in there?

The only way to know is to see an exploded diagram

This is assuming you have it bottomed out on the seat clamp?

Lateral thinking here, but I got a bit cut off my seat tube last year to alter the riding position by 10mm or so.

Daisy chain of cable ties from the seat rail to the frame?

I don't think there's an easy way to do it.

Get shorter cranks or a lower profile saddle, or a combo of the two...

Also grinding the lip off the seat clamp gained me an extra 3mm.

wll limiting the drop accomplish the same thing ? You can do that on a reverb with a collar they sell.

I suspect that on a reverb you could do it by setting the IFP in the wrong position deliberately. Not sure how reliable it would be though, or how far out you'd need to get it to limit the travel to a particular figure.

No idea how serviceable the brand X is though.

Expensive option but spacers are available for the 9point8 dropper to adjust travel to what ever you want.

On another thread, someone mentioned tying a bit of gear or brake cable between the bolt of the seat clamp and the bolt of the saddle which would limit extension.

Would look crap though.

Cable ties are not robust enough and will snap after a few post returns. I used a brake cable looped with an electrical screw block to secure (I've seen others use crimping) looped through seatpost clamp and seat. It worked fine for months on my sons bike until he grew enough to use the full drop.

Why not just use a BrandX 125mm dropper and accept 15mm less drop?  Seems the easiest solution...

Put the seatpost 10mm further into the frame, given it is the extension you are trying to reduce.

Seatpost is already as far into frame as it will go. Frame fits other wise (reach and stack)

I'll swap you for my 125mm Brand X then 😉

Non post modifying options include shorter cranks, thicker pedals and using a pipe cutter to take a bit off the seat tube.

Ive limited the extension on an external travel reverb (tricky) and on a RF Turbine (easy once I got the right spacer size).

Youll need to find an exploded diagram as stated above, and figure out what type of spacer will fit where.

Just tie a bit of dyneema between the saddle rail and the seat collar clamp?

I used a shoelace to limit the extension on my dropper, works a treat!