Is it practical to try to design a variable spring support or constant spring support for travel less than 0.1″?

It would not be recommended for a constant spring to be designed for less than 0.1″ for travel. Variable springs can accommodate that travel. The difference in load will be a function of the spring rate.

F-Type Variable Spring Designed For 1/16 Inch Vertical Travel And 1/8 Inch Horizontal Travel
F-Type Variable Spring designed for 1/16″ Vertical Travel and 1/8″ Horizontal Travel