That has to be the first time I've ever heard someone be advised to loosen a glow plug to make the engine turn over easier. I'm curious what having all that combustion pressure bearing on the loose plug does to the threads. Nothing good I'm sure.

If you can't crank the engine over as it is, then use a heat gun to warm the head before you start it. If you can crank it over and it's just difficult, then don't worry because you don't have a problem.