For example, if the asset has been added as artwork but it should have been leasehold, can the class ID on the asset be changed?
You can change the Class and Category at any time and only the account information is updated. If the “Auto-update Class, Category and Location” option is selected in the Setup screen and a change is made to either Class, Category, or Location on the parent, the children assets are updated as well.
If the asset was added as “artwork” but should have been added as “leasehold”, you will have to change the class and category and then update GL through the Asset Transactions screen if the module is set to Update GL.