You can't do it unfortunately. That's why it pops up a warning when you check it in the first place.
Ok seriously though there is a workaround for this. It's a total hack but may get you back to where you need to be without having to copy everything to a new sequence file.
WARNING: Not sure what versions of TS this will work with.
With the offending sequence file open go to Edit>>Sequence File Properties.
On the General tab change the File Format to XML.
Click OK.
Save the sequence file.
Now browse to where you saved the sequence file and open it with Notepad.
Search for FileGlobal and look for the offending variable. <MyGlobal classname='Num' valueflags='1'>
It should have a property called valueflags. It will be valueflags='1'.
Remove that property altogether. So it should be something like this: <MyGlobal classname='Num'>
Save it and reopen it in TestStand.
You may need to change it back to binary format from within TestStand.
If deleting it gives you problems then just change the valueflags to 0.
Hopefully this helps.
