Hey there,
Unfortunately we do not have this feature to given fixed amount of points in current system.
I have some ideas but I am not sure is it this is what you want :
1. Hard coded the fix point from the user profile page from the code file and disable all the point rules from
backend > Easysocial > points
2. Disable all the point rules from
backend > Easysocial > points, then only enable this point rules "User registers on the site" (command is user.registration), then set the fixed point inside this point rule, once the new member register into your site, they will only get this fix point 1 time only.