Simply put, the difference between preservation and restoration is whether or not you are removing material. That might seem like a “catch 22” but it really isn’t and here’s why:
With preservation you are taking an object and maintaining its current state through the use of things like rust inhibitors, resin sealants, clear coats, etc. You’re actually adding to the object in an attempt to keep it at its present state. This video here is a perfect example of preservation:
During restoration, more often than not you are actually removing material in the form of rust, metal, or whatever else is on the object. The goal of restoration is to bring the object back into a state that it can be used in some manner, either as originally intended or as something new. The following video is a good example of restoration:
Can the two be one in the same? Sure so long as during the restoration process you try to maintain the original look and feel of the item. One example would be removing the rust from an old hand plane, you simply remove the rust and try to achieve a like new appearance whether it’s for use or not. Sometimes an object may be so pitted that you need to add something like welds to fill in divots left from the rust, you would then grind these to meet the original surface. The overall goal would be to have the object look like you just walked into a store and there it is on the shelf.
Here is a video from over on YouTube that’s a good example of the mixture between preservation and restoration:
So as you can see, there’s quite a bit of difference in how you preserve or restore things but that being said, it is still possible to preserve something by restoring it.
Update 9/22/2023: While tooling around YouTube I came across this video which shows a typical hand plane restoration, after disassembly however, it becomes a preservation: