There have to be ways for the modeler to assign values to marks. Some implementations provide for graphical drag-and-drop allocation of model elements into folders that correspond with marks; others define an editor for the defined mark sets that can display all marks defined by the model for a selected model element, with pulldown menus for each of the marks. Another option is to define text files, and then use the large set of available editing, scripting, and awk-ing tools.
If the standard specifies a marking model language that can be stored in MOF, then the technology for accessing the marks and their marking models, storing them in a repository, and exchanging them with other tools will be the same as the one used for all other models and metamodels. This will make the sets of marks used by a mapping function just another input model.