I'm glad your dad is ok with what you want to do with the gun. When I'm gone my three sons will divide what I haven't already given them at that time but . . . if someone proves to disrespect how the guns should be maintained? All bets are off!
Why? Heck, I don't know! All I know it that I've babied 'em and kept 'em as pristine as I can. I understand that refinishing firearms almost always ruins their value and I know that as such they will be doing a foolish thing that will ruin the piece AND cost them money when they do the NEXT foolish thing . . . which is to then try to sell it. LOL
I'd try to do a little research and see what the original rear sight was and see then if someone makes INSERTS, front and rear for that issue range of front and rear sight that will light your fire. Then, acquire both original front and rear blades PLUS your latest and greatest preferred blades, i.e.: nightsights or whatever. Frankly, nightsights in a HP would be GREAT for self defense!
BTW, this same idea could be extended to entire sight assemblies I imagine, if you wish to go to fully adjustable rear sight systems.
Install the ones you like, save the originals in your safe . . . (uh, you DO have a safe I hope) . . . and you will be good to go until you trust it to your offspring in a few generations. By then this classic firearm will REALLY be uncool! LOL
One thing I truly believe you'll come to deeply regret . . .
One day that aftermarket finish will bug the crap out of you. It will scream "refinish" and folks will wonder just how rough that thing was before someone fished it out of the ocean and buffed it out. Doing this will absolutely kill its value to any collector, and only collectors pay top dollar for any fine handgun. If I saw it with a non-factory finish in a case I promise you my eye would not rest on it more than a tenth of a second, never to return for a second look.
Its your gun though, and PLENTY of fine High Powers out there will remain if you choose to do that to yours.