Hi,
as the title says - make it possible to change normal geologist into jolly geologist with 300 gems (regular price of Jolly Geo).
The reasons are obvious - you may want to replace your normal geologists with jolly ones for the sake of space in your star... and for the sake of science system.
Since Jolly Geos are unlimited, this does not change anything of gameplay, it's just a small feature to clean your star from unneccessary specialists. Once you have several Jolly Geos, especially when improved with books, you may want to dump the normal ones, since they become obsolete. You rather want to use your book-improved Jollies to find larger or faster deposits, and NOT want to use unimproved normal ones, which are slow anyway. At that point your normal scientifically untouched geos are pointless spots in your star, which you currently can't get rid of.
(Another option would be to make specialists be possible to "unhire", delete, return to inn.)