A valid offer of reasonable accommodation is an adjustment made to a job and/or work environment that enables a qualified handicapped person to perform the duties of that position.
Keep in mind that light and modified duty is not considered a reasonable accommodation by OPM for the purposes of Federal Disability Retirement.
If your agency is unable to reasonably accommodate you then you are in a great position to be approved for Federal Disability Retirement.
To learn more about Reasonable Accommodation click on the link below.