No idea, you have not answered the question
Before we can give you any useful help, we need you to answer the question I asked and tell us how you changed the key. (And seriously, if you did it in the database, then make sure you have your backup ready for restoration)
If no modifications were done, yes. If not, you may loose some info. As a rule of thumb, ALWAYS do a backup when you decide to dirty up your fingers and do things by hand. And test the modifications on a test system, don't do it directly in the production one.
Make sure you take Jira offline while you change the data back.
When you've done this, I'd strongly recommend re-indexing the system immediately after you restart it, and then running the integrity checker afterwards.
If you're lucky, you won't have too much damage and those two steps will leave your system stable and working.
There is a whole batch of SQL you can execute to change the project key, but you have to do it all offline, with backups, reindexing, integrity checks etc. You need to be immensely careful what you change to catch everything - off the top of my head (I know there's more than this), issues, project table, project custom keys, workflows, filters, comments, descriptions, raw text fields...
The standard way to change a project key is to create the new project, and then move any issues you want to use into it. That's completely supported and won't trash your system.
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