Is there a way to salt a whole potato before microwaving or baking it, I was thinking of soaking it in salty water but I doubt that would work, I need it to be seasoned on the inside not just the skin.
You cannot season a whole potato from the outside when baking or microwaving, the flavor may penetrate a small amount but most of the potato will be unseasoned. Boiling potatoes in salty water will give you a better result, however the skin of a whole potato will still block much of the flavor.
The only way I could think of to salt the inside of a whole potato would be so inject a salt solution into it with a syringe, which seems excessive. You'd probably be better off simply cutting the potato open after it's cooked and seasoning it then.