Question 1: Pokemon Ranger removes existing effects on Pokemon, including the one that prevents Tool cards from working. Since the effect is essentiall on the Pokemon, a Tool that comes into play after Pokemon Ranger is played would have its effect.
Question 2: The more well-known example of attached cards being "part" of a Pokemon is in regard to the Omega Barrier Ancient Trait, seen on Primal Groudon-EX and a few other cards. Playing Startling Megaphone would not remove a Tool from these Pokemon, nor would Crushing Hammer remove Energy, because one attached these are "part" of the Pokemon with Omega Barrier.
The reason Mew-EX can't use G Booster is due to the way G-Booster is worded. It states that the Genesect-EX that it's attached to "can use" G Booster, but Genesect-EX doesn't "own" the attack -- it's simply able to use it thanks to the Tool. This is how Mew-EX's Versatile Ability works as well -- its only actual attack is Replace, but Versatile lets it use the attacks of other Pokemon in play. A way to view this would be if Zoroark BREAK used Foul Play while your opponent had Mew-EX Active. Zoroark BREAK would only be able to use Replace.