Is there any way that could raise your legion fame so you can get the key for the legion safehouse, but at the same time to be able to have also the keys for the other safehouses?

PS. Currently i have the keys for NCR, Followers and BoS safehouses.

tnx

I dunno if you can "lose" a safehouse.
But in order to get Legion rep you need to do their (limited amount of) quests or you need NCR dogtags.
A way to get NCR dogtags without killing them is to go to locations where NCR vs ? battles are prone to happen then loot the dead NCR.
It will take a long time though but it's a secure way to get good rep with both Legion and NCR.
You need to talk to Lucius at The Fort though.
Don't know if you need to advance to a certain point in their quest line though.

tnx for the info

Wikia said this "Lucius will give you the key when you are "liked" by the Legion."
So you don't need [Idolized] status.

i know, but i have to become "liked" and in my current playtrough it will not be so easy.

There are a number of ways to gain rep with them, without losing it with the NCR.

Dogtags. Either loot them off already dead troopers, or pickpocket them.
Teach the Decanus in Cottonwood Cove how to disarm mines. You'll need a bit of explosives skill to teach him.
Save Martina Groesbeck or whatever her name is for Vulpes, and then help Cpt. Curtis blow up the Monorail at Mcarran. If you do it right you should be able to not lose rep with the NCR.
Get a firing mechanism for the howitzer in the fort.