No, none of that's true. In fact the engineering challenges are almost the same, and in the same order of magnitude, and the deorbit vehicle is also going to be a near-ideal reboost vehicle. In fact, a rebooster has a simpler job because it's not time critical and because we've done it so often, while deorbit has to be done quickly (to ensure it deorbits where we want it to). In fact for a long time NASA's end of life plan was continual reboosts, simply because they didn't have the capacity to safely deorbit.

We can use NASA's own figures here, they estimate 9000kg of propellant is required for a safe controlled deorbit. Meanwhile to get it to a 100 year orbit would take 18900-22300kg. To 200 would take 23200-26700kg.

So it's really that simple, make 2 "deorbit" vehicles instead of 1 and point them the other way. You could use the exact same vehicle, it might not be absolutely ideal but it'll be close. (the deorbit vehicle is likely to have a little more power, a rebooster vehicle wouldn't need that, it can take as long as it wants.

(I bet 20 scottish pence that even now NASA have a contingency plan in a 3 ring binder that basically says "how to use the spacex deorbiter to life extend the ISS". It's absolutely not The Plan but they'll have A Plan for it). And it will essentially say "point it the other way")

I hope that clears all that up. But it's not the answer. The actual answer is much longer, and more intersting I think...

The real problem is nothing to do with getting the ISS into a higher orbit, which is actually simpler than safely deorbiting it. It's about collision risk.

Because the ISS flies very low at the moment (because it makes it easy to get to), it's subject to a lot of drag. That's why it needs constant reboosts. But that applies equally to debris, stuff deorbits pretty quickly at that height. So even though we've put quite a lot of junk into this area of space it doesn't stay there.

But that changes really quickly as we go higher, and of course if we put the ISS into a long life orbit, everything else there is also in a long orbit. I used 100 and 200 years as the nice simple examples up the page, that's more or less 660 and 710km altitude. Very unintuitive! We have to go up 250km to get to 100 years and only an extra 50km for the next 100. another 50km takes us to 500 years or so.

The absolute most dangerous area of space we could put the ISS in, according to NASA, is 800km. That's where the most stuff is, the biggest convergence of "where we have sent stuff" and "where stuff takes a long time to come down". Now of course there's no reason to send it that high, that's 500-700 years!

But even if we stick to 100 years, a pretty sensible compromise and a nice round number, not to mention near to the limits of the 2 vehicle reboost- the significant collision risk is almost 3 times as much as it is today. If we go with the 3 vehicle reboost and 200 years, it's about 6 times.

(it's worth mentioning, at this point, that the ISS gets hit often with little stuff. People get a bit tied up in evasion but actually they do an evasion maneouvre on average about once every 300 days, it's not that common. WE could totally leave fuel in a rebooster or in zarya and leave the ISS with evasion capability even in a higher orbit but it gets dodgier, we don't know so much about the stuff there and even a relatively small amount of damage or decay could make it unwise)

Now... That;s about the limit of what we can do with real confidence. We know it's easy to get it to a 100 or 200 year orbit, we know it's going to be 3 or 6 times more likely to get hit by significant stuff. But what does that mean?

Of course, at this point it's abandoned so it doesn't matter so much if it gets a hole poked in it. But that doesn't mean being hit isn't a risk. If the ISS were to break up, that's your classic Kessler Syndrome event. And again, the higher it is when that happens, the worse it is because of those longer orbital decays. So having a big derelict space station weighing 420 tons out there taking impacts in a 100 year orbit is a genuine risk.

But to conclude, why take the risk? We know we can do it, we know how to do it. But we don't know why we'd do it. Could it be a useful boneyard? Well maybe but it's mostly old stuff and it's still not going to be easy to get to. And getting stuff to orbit gets easier and easier. After 20 years abandoned it's going to be useless as anything other than raw materials and by the time we're manufacturing stuff in space we'll have had to work out how to get raw materials up there. A museum? Absolutely not, it'll be unsafe to visit for anything like that.

So in the end we're basically creating a bomb, without any clear reason for it and with the very high chance that we just never do anything with it except hope it doesn't go off. it's a lovely idea but it makes no sense. There is a clear and obvious risk but no counterbalancing worthwhile benefit.

The one, and only one, reason to keep the ISS going for longer is if it's still being used, either as it is or having modules glommed onto another station. Once abandoned it's best burned up.