by just changing the lowers??

eg revelation 26 to 29?

I’d imagine anything inside which previously went from one end to the other wouldn’t really matter and could be left unterminated two inches from the bottom. 🙄

You would lose a lot of available travel as the damper rod and bottom of the air spring dictate the maximum axle-to-crown, (ie your a-c will still be the same as the with the old 26″ lowers on, and the amount of stanchion showing will be about 35mm less than it was), and as an absolutely critical safety feature, you would also need some way of putting a spacer/bump stop inside the positive air spring chamber to stop the wheel fouling/catching on the crown when the fork is compressed. (maverick do this but I don’t think their spacer kit would be bodge-able into a rockshox fork). Even if you managed all that safely your 150mm 26″ fork would end up being about an 80mm 29er one.

More trouble/cost/risk than it’s worth imho.

I’ll take that as a no then!

was kind of wondering if just the Arch was higher but obviously not!

I’m not sure the height of the arch relative to the height of the dust seals really matters, the damper rod and air spring lower rod length will still limit the overall axle-to-crown, and you still need something to stop the front wheel suddenly stopping as it catches the fork crown.

Yes you can swap the lowers. Tazzymtb off here has done it with rockshox. You do lose travel I think about 30-40mm worth and need to use a longer travel 26″ crown steerer unit like a Revelation

EDIT Cant use 26er lowers with 29er wheel

I thought the only difference between the 29 & 26 was a 1.5 inch extension on the bottom of the fork.