The tubes are gonna have to come off to put a new valve cover, more importantly, do you really need a new valve cover? I just had mine off, I think there was a rubbery ring inside the cover that slips over the metal injector ring. I'm trying to find a "part" on google but nothing I recognise is coming up. Apparently the fuel tubes are "single use items" but I've reused mine a couple of times
FWIW, I also fully greased my valve cover gasket, mainly to make it stick in the valve cover when right side up so the gasket doesn't fall out and go astray, I also put about 12-13nm. 11 didn't feel enough.
Edit: just found out the injector seals cannot be purchased seperately, you have to buy the whole cover for $643
Also don't over tighten the glow plug nuts, I snapped one and had to put an old one back in, turns out I had two which were worn out