#1). SAFETY!!! O.K. You move the shoulder back on a rimless and you create excessive headspace and if you use the case in ordinary circumstances, you could have it pull apart, release hot/dangerous gases and do yourself harm... BIG TIME!. So my first question is "why?" thank you.
#2). As said, if you are using ordinary shell holder/dies for an ordinary cartridge, you can do this by shortening the die (or the shell holder) but that would impair the use fullness of the die or shell holder in the future unless you are carefull... Some die makers warn about using their dies with other brands of shell holders BECAUSE they were not well standardized... Not an unwarrented warning,l and it sold more shell holders for the die maker... (ha, ha, ha... )
#3). If you are getting extremely froggy and experimenting... About any standard, WELL lubricated method can be employed. Imperial Die Wax helps alot. Cutting off used dies bought cheap and 2nd hand at a gun show, no problem. .2? As much as you want. If you want to reform the "head" of the case where the rim is, then you need a lot more press strength. RCBS is famous for case forming dies. Well advertised. Most other makers have them too. Making .250 (or .22/250's) from .30/'06 was common [BUT a lot of work...] At one time, RCBS would mail you the form die instructions for an SASE... Obviously, more details of your "scheme" more detailed advice... Luck.