I’m all for fixing what I can but I’ll be the first to tell you sometimes I’m like the guy Dirty Harry blew up at the end of Magnum Force (he didn’t know his own limitations). That said, many manufacturers will make their repair parts available with the stipulation that if my cousin’s nephew’s pool boy’s girlfriend said to ‘change the flux capacitor’—and that wasn’t actually the problem—I have to keep the part, good or bad-no returns. (and I’m ok with that)
Most manufacturers will, yes. The issue lies in companies like apple, deere, etc. that program in the individual parts serial numbers for anything that talks to the computer, or not selling you a computer that allows you to read codes unless you are an "authorized mechanic." That makes it so you have to go through them to get your stuff back up and running.
The only excuse that I have heard from Deere about implementing their lockout is the software is "proprietary", to stay within environmental regs and to keep the equipment performing at their designed capacities. Both of the later are bogus because once the equipment leaves their doors it is no longer their responsibility that the equipment meet either of those (unless there is a design/manufacturing issue/defect). So it isn't Deere's problem if Uncle Billy goes in and blows up his motor or does nothing but rolls coal because he decided to screw with the tune. The third is bogus because they can sell a tablet that talks to the computer without releasing any source code. What they have done found a way to force customers through their shops for every repair that involves a plug.
Don't get me wrong I am ok with technology being added and companies protecting their proprietary stuff but they should be required to sell whatever tools are needed to repair or work on their equipment to anyone who wants to buy it regardless of whatever bogus schooling your company thinks is needed.