Does anyone know if u can change the class every time(with an editor) when some stonghold comes up so u can get all of them???

I just tested this, and no, you can't. It is set in stone based on the char you make at the beginning of the story. I started as a monk, then dumped him for a ranger/Cleric dual, and I still got the keep instead of the Ranger stronghold. I also switched to a mage to try and get the mage stronghold, but no dice.

You can change class, but you are only allowed one. As soon as you choose one, you cannot get another.

no i mean using an editor like shadowkeeper

What about a dueled class ? If I get the fighter stronghold and then duel class to mage, could i get the mage tower ?

well it is possible to get both the thief stronghold and the warrior stronghold with a dual class char. go for the thief stronghold, kill Mae Var but do NOT go back to Renal.
Go do the Nalia keep and oen of the options she gives you will let you come back later if you change your mind. Then go claim the thief guild from Renal, and then run back to Nalia to get the warrior keep. (I heard from someone earlier that if you take too long getting back to Nalia it is too late and you can't get it.) While you do get to control your thieves and make money from the guild, I found I only got 2 side quests from teh thief guild, but the full spectrum from the keep. Not having played a pure thief I am not sure how many thief side quests there are supposed to be.

Unfortunately there's only two sidequests to the thieves' guild.

I posted a reply to something like this somewhere else.
You can input SetGlobal("PlayerHasStronghold", "GLOBAL", 0) into the CLUA console after you get your first stronghold, and then you can get another one. If you use Shadowkeeper to change your class you can get all the strongholds.

this is strange
when i went through as a fighter dualed to a thief, i did the thief guide first (fighter class still inactive) and got it. I then did the keep quest (fighter class active) and nalia offered me the keep. i didn't use shadowkeeper to modify any of the stuff except for the kit and race. maybe it has something to do with active classes.

a side note about dual classing. did anyone loose there proficiences for the first class. it doesn't show any of them or give me credit for them. (shadowkeeper fixed this as well, but looks bad as my thief has twice as many proficiences as he should)

You lose them at first, and get them back when your first class becomes active again.