Oof definetely don't heat and reshape needles. When you apply heat like that you're compromising the bonds in the metal and its gonna become brittle as all hell. The chances of it popping off in you or bending are way higher.
I always hated reusing rigs but sometimes i was forced to. For a while the place i lived didnt have an exchange, and depite the fact it was legal to have and sell them, most of the pharmacies in the state were corporate and had blanket bans on selling them. I used to buy from them for years, until i went in one day and my usual counter guy told me they arent allowed to sell them without a script anymore, store policy.
When i lived in NC i smuggled one needle i got in vermont when i went on vacation there, and i used it for months. It was horrific. All the numbers came off, the plunger was so worn that you had to lube it up or it would just pop off in the barrel. Eventually i figured out farm stores sell them without scripts there, but the gauges were way big.
God, unfortunate near-lifelong resident of NC here... I remember the bad old days of being an IV user in this state. Started IVing in 2007 and just as you say, even back then you didn't have to have a prescription - they were legal to possess, although prior to many further protections in place now, it was damn near impossible to find a pharmacy that would sell them without one, and needle exchanges were still illegal at the time.
I remember occasions trying the whole "my mom's diabetic, but she's bedridden" routine, it occasionally working but usually not. Even a couple times showing the pharmacist my battered, scuffed and rubbed blank rig with the crooked, dull tip, and a matchbook to sharpen it with, and explaining to them that one way or another, I was using a needle when I left, and I would really, REALLY appreciate it if they would sell me some clean ones. That usually worked, though a bit much maybe lol.
But prison was especially bad. I wasn't shooting up in there, but Jesus Christ. I'm talking guys literally STANDING IN LINE 7 or 8 deep to use the same rig, to shoot either suboxone or meth, with 10 minutes to finish everyone and nothing but a cup of hot water and a bottle of surgical scrub...
Definitely done my dirt on that front tho, many many times. Extremely lucky to have only contacted Hep C, and that cured with minimal damage.