Let (xr,yr,zr) be the position of an atom when the command
CONS HARM FORCE 24.0
The constraint energy for this atom when it later is at another position (x,y,z) is:
EC=24.0 * ( (x-xr)**2 + (y-yr)**2 + (z-zr)**2 )
and the force will be the negative gradient of this expression.
I do not know what this will do to your protein, but it will take a strong force to move this atom more than an Angstrom or so from the reference position (xr,yr,zr), and with force constant 100 the atom will be even more firmly attached.