Actually is it possible to re-link Trailhead profile to another developer-edition organization? If you know how can I contact Trailhead support, that would be nice.
Yes, you can "merge" your existing account to a new account. Note that the change is irreversible. See this answer for more info, but I'll include the essential text here.
Before We Begin
The following process assumes that the learner can still log into both the ‘from’ and ‘to’ Trailhead accounts. If the learner can no longer access the ‘from’ Trailhead account (e.g. they can no longer use their previous corporate login for Salesforce), we, unfortunately, cannot process the merge request.
One more thing (this time for realz)
Please note that the process of transferring Trailhead points and badges from one account to another is irreversible. Once this transfer/merge happens, there is no way for the learner to reverse the process and move their Trailhead points/badges back to the original account.
What we need to initiate the merge process
In order to transfer/merge Trailhead accounts, we need 2 things:
(1) The user id for the ‘from’ Trailhead account
To get this information, do the following:
Login to the ‘from’ Trailhead account - the one you want to ‘give up’ and move points/badges from.
Click on the ‘My Trailhead Account’ link under your name.
Copy the value after the ‘userId=xxxx’ portion of the URL. This is the ‘from’ user id.
(2) The user id for the ‘to’ Trailhead account
Repeat the steps above to get the user id for the ‘to’ Trailhead account - the account that you want the points/badges transferred to.
Requesting the account merge
Once you have the ‘from’ and ‘to’ user ids for your Trailhead account, please send an email to email@example.com with the ’Account merge’ subject line (mailto:firstname.lastname@example.org?subject=Account merge) and include the two ids. We will be in touch with you as soon as the merge process is complete.