Making an Excel File Read Only when a power point it's linked to is in use?

Is that possible?

To make an excel file Read Only once a powerpoint which it's linked to is in use.
To save potential crashes if it's updated whilst a presentation is taking place.

Just a theory here, assuming that the spreadsheet is shared over a network, if you open the spreadsheet on the same terminal as the presentation, does power point look at the local instance instead of the network? If it does then that might eliminate the need to make it read only.

Other than that, I think that you would have to open and unshare it, but then anyone who already has it open would have to 'save as' so you could end up with data that should be in one place scattered in multiple files.