If you want to perform design changes in a db (doesn't matter if it's a back end or *front end) you should open it exclusively. You don't do this by opening from any 'recent files' list.
If you don't you run the risk of performing changes only to find you cannot save them, are blocked from even starting the changes, or inducing corruption from conflicts. Thus it doesn't matter if the tables are linked or not. If you're performing design changes on tables, there's no need to un-link them. This statement
to change the structure (add fields, relationships, change data type...)
raises a little red flag. It's one thing to add table fields because your original schema overlooked some attribute of an entity in your project. It's another thing altogether to be adding fields for similar attributes when that data should be in rows in its own table. Not sure what your statement means.
* - I'm not advocating sharing a single FE here, just saying it doesn't matter about how either should be opened.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.