For Alt-specific designs, the only thing you need to remember in SMRT is that to specify an attribute level that doesn't apply to a particular product concept, you actually type "NA" for not applicable into the product definition interface. So, just import your attributes, levels, and utilities using the standard format in a .hbu file.
For piece-wise price estimates that you have computed on your own, follow the same trick we use when moving piece-wise price functions from ACBC to SMRT for market simulation. Since you set up your own piece-wise coding, you know what your endpoints and cutpoints were for your price function. Simply compute the discrete utility associated with each endpoint and cutpoint, write those into your .hbu file, and pretend that these were discrete utilities along a standard dummy-coded (part-worth) price function. Just move the discrete utilities for these price points from the .hbu into SMRT (importing into SMRT using Analysis + Run Manager + Import) as if they were discrete levels of price in a standard conjoint design. SMRT will be able to interpolate between any of the price points using straightline interpolation, which is true to the underlying piecewise function anyway, so you are good to go.