Perturbation can take two forms. The first involves a radial redistribution of the psf probability. For each psf evaluated scales the values by the corresponding value in the perturbation profile, where the values in that profile correspond to radial bins about the psf centre. This technique has that advantage that fine scale structure in the psf is preserved, as is the total normalisation in the area being evaluated. The perturbation profile that you supply is a mulitiplicative factor in for pixels in the radial profile. SPRESP does not check the axis values of this profile.
The second perturbation mode is smoothing. The perturbation file you supply is a 2-D data file, each of whose dimensions are odd. The evaluated psf is convolved with this file.