You can modify what the project parameter applies to, or what group it is in, but not the name nor the data type of the parameter. If you want to change one of those properties, you have to delete the parameter and create a new one.

So bad, I accidently chose "Integer" instead of "Text" and constrain that parameter with formulas. Is the some add-in that can fix this?

1) I doubt if there is a way.
2) Even if you COULD change the parameter from integer to text, if this parameter is being used in existing formulas I don't think the forumulas would work anymore once the parameter type changed (assuming they're working now). Or are you saying that the value of the parameter is controlled by A formula?

If you meant to use text you may find you can't use it in the formula you created anyway. Not many formulas that work on text data. Create the new version of the parameter and then see if you can replace the reference to the old one with the new one. Then remove the wrong one.

Fwiw, if you did that in Access (database software) you could change it but you would lose all the data stored in it. Revit goes one step further and makes us start over. It's a fundamental thing, we have to choose the correct Type of Data at the outset. Edit: I had occasion to use Access today and I find that I can't change the type of data, just delete it now, like Revit.

It is hard for the sort of person who creates and manages databases professionally to accept that I will potentially store thousands of records in a field (parameter) yet can't figure out what type of information I need to put in it first, or be more careful while doing so. Yes, it is rigid thinking but creating a reliable database isn't trivial.