How do I add/change parameters without messing up old projects that used my effect?

I clearly want to  update my plugins after a while and that includes adding new parameters or replacing old parameters with new ones of different types. Question is, how do I do that without corrupting old projects? Currently I made a copy of my code and I have both the old version and the new version with different parameters just to prevent breaking my old projects. The downside is that I had to modify the name of the plugins (added 2.0 at the end) and also the old plugins obviously don’t get the actual functionality update(s). How can add/replace parameters without breaking old projects? Is the only way to keep the old parameters as invisible/hidden and read their values to adapt the new ones? That makes the code very messy.