The application is a spring to extend double acting cylinder. The spring force is not adequate to keep the cylinder extended.
I want to constantly apply 80% of the available pneumatic pressure to cap end of the cylinder to assist the spring in maintain the cylinder in the extend mode.
Presumably the piston rod area and the force of the spring are only equal to 90% of the available pneumatic pressure and there is ample volume that when the cylinder is forced to the retract position the extend pressure is minimally effected.
When retracting the cylinder 100% of the pneumatic pressure would be applied to the rod end of the cylinder.
Knowing my percentages are not precise and that I would be able to regulate them with ease is there likely to be any pneumatic or mechanical negative consequence of applying a constant pressure to the cap end of the cylinder.

S. Jackson,

There will be no negative effect mechanically. However, it is a little inefficient to have air on the spring side.