Chances are that long scale strings left uncut will have the main body of the string wrapping around the peghead, setting up possible breakage. Cutting the string itself could cause possible unraveling, but Mike Watt cuts off D'Addario longscale strings to use on his Gibson shortscale all the time, so have a go and see.....
If you want to buy shortscale strings then I would go to
WWW.juststrings.com or
www.bpstrings.com for a very wide selection of shorty strings. They can be had in just about every type and gauge their longer brothers can be had in.
My favorite shortscale strings currently are the SIT Power Round Nickels and D'Addario flats.