So most modern handguns out right now have the 10-round magazine options for states like us that have a limit. What about guns that never had a 10-round magazine made, is it possible to have the high-cap mags blocked/pinned/welded/whatever to keep it 10 rounds so I buy the handgun and bring it into Hawaii?

Atates like Hawaii and others requir "permanent" measures to block/restrict capacity.  Initially there was only one gun store that "welded" blocks inside magazines to meet compliacne.

I would suggest you just store your current mags and buy some 10's, it'll be a whole lot easiers and less hassles.  Most manufacturers produce 10 cap mags so people can be in compliance with Kommunistic States.  Otherwise there are aftermarket options.  Whatever you do, stay FAR away from ProMags, they are only reliable for malfunction drills.  MecGar is reputable and actually are contracted by several manufacturers to produce OEM mags.  SigArms and Beretta among others.  What do you have?

Well that's the issue. I don't own the gun, wanted to bid/buy one off of Gunbroker but after doing some searching online the STAR MEGASTAR handguns never seemed to have 10 round factory or aftermarket magazines. The company is gone now so no real aftermarket support for rare/obscure pistols.

The MEGASTAR comes in .45 ACP and 10mm AUTO, but respectively at 12 and 14 round magazine capacity only. That's why I didn't bid on one yet cause I could have the handgun shipped without a magazine but I wouldn't be able to find any magazines to use in it to be compliant.

"Permanent" is inaccurate.

This subsection shall not apply to magazines originally designed to accept more than ten rounds of ammunition which have been modified to accept no more than ten rounds and which are not capable of being readily restored to a capacity of more than ten rounds

You do not have to make a permanent change to the mag.  Case law indicates that if you have to disassemble the mag, it is "not capable of being readily restored"

"Permanent" is inaccurate.

Quote from:  HRS 134-8

This subsection shall not apply to magazines originally designed to accept more than ten rounds of ammunition which have been modified to accept no more than ten rounds and which are not capable of being readily restored to a capacity of more than ten rounds

You do not have to make a permanent change to the mag.  Case law indicates that if you have to disassemble the mag, it is "not capable of being readily restored"

Okay clearing the legal jargon, what exactly does it mean? I can have the magazines if I have a block installed in them limiting it to 10 rounds?

Yes.