There are a few things to be careful of when changing the image surface value.

First, if the field type is either real or paraxial image height, the field type is changed to angle or object height for infinite or finite conjugate systems, respectively. The angles and heights used correspond to the primary wavelength chief ray angles and heights as computed for the unaltered system.

Secondly, imagine a system where you set the image surface to be prior to the currently defined stop surface. ZEMAX moves the stop surface to a (possibly virtual) dummy space prior to the existing surface 1. Unless the system aperture is object space numerical aperture or cone angle, the system aperture is changed to entrance pupil diameter, and the aperture value is set equal to the original paraxial entrance pupil diameter computed for the original stop position. Note this assumption might not be valid for systems that require ray aiming.

An alternative method for computing system performance on multiple surfaces is to use multiple configurations. In the MC editor, click on Tools >  Make Conjugate. This tool lets you re-define the object, stop and image surfaces, plus make any desired changes to system aperture, field definitions, use of ray-aiming etc that you need.