For FOX depends on the model year. The air spring was changed in the past few years. New models need a new air spring. Old model like the 36 29er I have the air spring is adjustable with a few tools and some FOX fluid.
No idea about RS.
Thought this was about the new 36 and Lyrik 29er 170mm forks which appear to be Vapourware at the moment.
Realize that the earlier 36 requires tools to adjust travel and the other one requires a new air spring. Factor in a new air spring and servicing of the fork with cost of purchase.
RS forks will definitely reduce to 160. You need a different air shaft, which is about a $50 part. Doing the install requires dropping the lowers and is a pretty easy job to do yourself, though you'll need snap ring pliers.
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