Say I import a mesh and then add quite a few properties to it and such. Then say the original mesh gets updated and I need to import it again. Is there a way to replace the existing mesh with an imported one so I don’t lose my properties and such?
Depends which properties. You can Link any Mesh to any other Mesh Object by selecting (say the imported) mesh from the dropdown in the ME: field in Links and Materials tab in F9. You can then Copy existing properties from another (Active) mesh with Ctrl-C or make links to them from Ctrl-L. (Properties in Ctrl-C are actually a GameEngine DataSet but I’ll assume by properties you mean Mesh or Object attributes).