There isn't a short cut method of importing the I/O table, since opening a new file will erase the current I/O table. But if you really have a lot of I/O to merge, try a text editor to copy the I/O label declaration part from the file whose I/o you want to copy from and paste into the current file.
Frankly we don't recommend anyone to edit the file using a text editor because a mistake in the format can render the file unreadable by TRiLOGI (so please back up your original files before doing something like this!). But for those who have special needs this may offer a possible way but again please use it with caution, and at your own risk!