Old o-ring getting stuck left behind isn't really a thing afaik but if it is then clean it off. Blow the dirt off around the injectors the best you can and spray a bit of lube or rust penetrant around each one before you pull them/the rail out. It might take some wiggling or even prying so a bit careful with that. That's IF the problem is even that.
Maybe pay attention to which way the clips are on because sometimes that matters and of course lube the new rings.