How to force installation of standard-width blinds for window with nonstandard dimensions?
Those 27 inch blinds you link to are top mount and will fit in a 27.5 inch opening without modification. But there are also side mount ones that would also work but you would need to add a 1/4 inch shim to both sides or a 1/2 inch shim to one side.

Most blinds can't be simply cut down in width except those that are designed to be cut to length.