I have seen no legislation and believe none exists regarding the good time increasing to 40% for Kansas felonies of any level. Additionally, the last time there was an increase in the good time percentage the change was not retro active, it seems unlikely that would change for any future modification. So, since your boyfriend has already been sentenced it would not apply to him if it did exist.
The DOC (Department of Corrections/Prison) will not let him out earlier then his 80% of 180 days. There is a chance he will not be moved to the DOC or prison; instead, he would stay in the county jail until he gets into his good time, receive his DOC number and be released on post-release. This is probably what the deputy sheriff was trying to explain and is a possibility for short sentences. The reason is because the firststep in the prison sysytem is to spend time in the diagnostic unit where they determine what facility a prisoner should be housed. It can take a couple of months. That is a lot of effort wasted for short sentences and sometimes the inmate will just stay in county.
The Judge loses jurisdiction to modify a felony sentence after the sentencing in Kansas, except for probation violations. As a result, there will be no way to now go back and ask for probation. Plus, if it was part of the deal to not ask for probation, it would violate the plea negotiations to now ask for probation.