i have filled out the form to join waves signature campaign, then posted 50 posts already as required, but still in 'to be reviewed' status.
the question is: can i change my signature now?
Not if you would like to stay in the campaign. The campaign isn't over until the ICO is finished, not whenever you have made 50 posts.
Check with Ahmed Ashraf on slack. I believe it is he who updates the signature campaign list.
