On Trace de Trail, you have access to two different pages to create a track: the rapid mode or the expert mode.
In rapid mode, you have access to few parameters : the method for calculating the ascent uses the ASTER GDEM digital terrain model. The elevations of your input file are not used.
If you want to choose the calculation method or customize your track with photos, points of interest or a description, you must choose the expert mode.
If you have created your trace in rapid mode, you can still modify it and find all the options of expert mode. Even if you calculated the profile using a DEM, if your input gpx had altitudes, these were saved and can be used later.