Is there a way I can buy something from the marketplace and if it doesn’t support the engine I am using that I could manually do something to the item I brought to make it support my engine?
If the product is just meshes and fairly basic materials, you can use it in a wide range of engine versions. If it has a lot of version specific code ( blueprint or C++ ), of course it won’t work in the wrong engine version.
I can’t recall the option in the launcher, but it is possible to make it install the product even when it thinks the version is incorrect. In the worst case, you can install the engine version the product needs and then migrate it to you current project.