There's enough advice out there to tell you it's a bad idea.
Springers have grease to lubricate the action + piston head. Adding oil/WD40 does nothing except to upset the lubrication balance.
Why do you suppose they removed the advice from the kit?
You're ruining your rifle with a misplaced sense of goodwill. You're also risking being caught with an illegal rifle.
If you think there's good sense to carry on as you are, then it's your lookout.