Before you go unloading and cutting down your Hilti caps, keep in mind that the priming compound probably coats at least 1/2 of the shell. I know that it certainly does with 22 long rifle shells. I would consider it fairly risky trying to remove the powder from a Hilti cap and don't see the need to shorten them; you can punch out the fired case fairly easily. I also don't agree that you need to unload the caps in the first place. It would not surprise me if a loaded cap in an offset case might be adequate for plinking, without any powder added to the case
If flying in black powder is a problem, check on Trail Boss and see if it can be flown in. I think most or all of the smokeless powders would be fairly risky in an antique rimfire case. If you do use it, I would use it sparingly and put a pinch of drier lint on top of the powder to keep it close to the primer. Without something to keep the powder close to the primer, I think you will get highly variable pressures
cheers mooncoon