I agree with David:
The current mass is shown by the system mass parameter and the original mass probably has been just added as a fix text or it exists as a parameter in the model that does not change during modification of the model.
For example you can use a relation old_mass = pro_mp_mass to assign the valuevalue, then comment the line for later use (if you want to make another mass the current one, just uncommment and verify relations).
Gunter