Now that's very possible.

Colt is a company you never say never about.
You could order about any barrel length you wanted, but they are considered "special" and you dang sure would want a letter on any barrel different from standard.

Some worthless Colt SAA trivia for ya,
7.5" barrels from 1873 thru today
5.5" barrels introduced in 1875
4.75" barrels introduced in 1879