How to merge multiple ttx files

mitradranirban

I am creating some variable color font using Fontforge and fontmake. In the final stage I need to merge variable font with the CPAL and COLR tables which are manually created to create the color variable font. I am using fonttools  ttx for the merge. In ttx documentation there is a option to merge a ttf file with ttx, but how to merge multiple ttx files? I am currently doing manually by copy paste in an xml editor.