6UPLABEL: modifypair - UPLABEL command

Parameters: front=<string>
            rear =<string>
            sched=<integer>
            rank =<integer>

Front designates the C13 - atom of the Amino acid pair, 
Rear the N15 - Atom of the pair. Sched is the schedule number, 
the binary representation of the labeling pattern. 
E.g. : The pattern X_X has the schedule number (2^0+2^2)= 5.
Rank is the slot of the labeling scheme.

