I’ve not got a yari (but would like one – or a pike)but have RS Revelations. If the yari is anything like it, most of them will have the same length stanchions but will just have different length airshafts. I recently changed from 130mm travel to 150mm travel. Think the part was £27. I got Bad Ass Bikes near Bristol to change the part for me (as I don’t have circlip pliers / spare fork oil etc).
The stanchions are marked all the way round with various travel and sag setting lines depending on what airshaft is fitted.
I know it’s not meant to be difficult to do but I just cba to do it. Thought their all in price for £60 was great. Forks are much plusher since it was done as they did a lower leg service effectively at the same time.