There should be no problem.
The Leopold keycaps are the same size and thickness as Cherry's own keycaps which can be mounted on Cherry MX switches in any of four orientations.
There could sometimes be problems with mounting thick keycaps (such as Cherry double-shot) on keyboards with Costar-style stabilisers, but the POK3R has Cherry-style stabilisers.
I use Leopold keycaps on a Ducky keyboard with "upside-down" Cherry MX switches and Cherry stabilisers with no problems.
BTW, from what I have seen the non-backlit POK3R should come with some nice thick PBT keycaps from the start. Getting Leopold caps might not be an upgrade.
BTW2. Be sure to get a keycap puller if you don't already have one. It helps a great deal to have one when swapping keycaps.