Can i go from implants over dentures to all on four permanent?

You would need to have some implants towards the back of you mouth.  Most denture retaining implants are placed near the front.  So, the answer is yes, but you may need additional implants.

While it would be fantastic to say that having 4 implants already means you can just make a bridge to attach, but often that is not possible. The biggest reason is what is called the transition line. This is the line where the restoration becomes your gum tissues. Ideally, this is hidden by your lips, but that isn't a consideration when creating the snap in denture because the "flange" of the denture can be made long enough to hide the tissues. If the implants weren't placed deep enough, and the bone wasn't flattened when placed, then it is possible you would need to remove all the implants and start over.

Yes, you can convert to all on 4 but would need to plan for more implants and get a ct scan to find the proper position of the future implants.