[gmx-users] How to change to heavyh in an equilibrated system

[Ramon Crehuet]

Dear all, 
For testing reasons, I would like to compare a system that I have setup using heavy hydrogens (-heavyh option in pdb2gmx) to exactly the same system without using heavy hydrogens. 
I could redo all the system setup starting from the pdb2gmx, but I would like to avoid that. That setup was tedious and I would like to start from the exactly the same coordinate file. 
I could write a script to change the atom masses in the .itp files, but again, this doesn't seem the easiest way. 
Is there a way to generate a new topology from the equilibrated .gro or .tpr file? (when simply feeding these files to pdb2gmx the ions are not recognized). 
Thanks! 
Ramon