Hey
Is there any way to add custom traits as Club Requirements without replacing the club_tuning XML file????

None that I can see. This tuning would likely be a good candidate for a script injection method for the tuning as only one mod would be able to override that data. Lists like that are generally fairly easy to update within the scripting but as I don't have GT I wouldn't be able to try it out myself. It would have to work something like the InventoryType method - http://modthesims.info/showthread.php?t=571603 (but should be easier) and I'd be willing to help out with advice if someone wants to try tackling that.

I will try to do it myself.
I've been fiddling a lot with TS4 script files and Python tutorials lately.
If some experienced Python scripter knows how to do something like this, please, give it a try! :D

you're going to need to edit the clubs.club_tuning file in s4studio. There's a section named <L n="CLUB_TRAITS">, which is a list of the applicable traits to filter clubs against. simply add a new line and replace the number ( <T>9620<!--trait_Snob--></T>)
with your trait number. That number is found in your trait package under the trait tuning, looks something like s="14463942914636423222".
it's a good rule of thumb to comment the number as well, since it makes changes later much easier, since you can trigger a new trait number when modifying or recreating your trait.
Happy modding!

similarly, if you want to make a trait similar to the 'bro' or 'snob' conditional group buffs, you can include that same trait number in the proximity test/trait test section of the mod constructor. neat things are neat.

edit: because bad typing

Maybe read the first post again? They are specifically asking how to do that "without replacing the club_tuning XML file".

Couldn't do it....it's just too complicated :P
I guess i'll have to edit the club_tuning file until someone figures it out