Use MergeFonts() function to merge font glyphs. The following example shows how to merge A.ttf to B.ttf and generate C.ttf.

Open("A.ttf");
MergeFonts("B.ttf");
SetFontNames("Font-Family-Regular", "Font Name", "Font Family Regular", "Regular", ""/*copyright notice*/);
Generate("C.ttf", "", 4/* remove bitmap */);

I want to replace also some A.ttf's glyphs with B.ttf's glyphs. Before MergeFonts() function called, remove the glyphs I want to replace. The following example shows how to do it.

Open("A.ttf");
Select(0u0020, 0u00FF);
Cut(); # delete all of latin-1 chars
MergeFonts("B.ttf");
SetFontNames("Font-Family-Regular", "Font Name", "Font Family Regular", "Regular", ""/*copyright notice*/);
Generate("C.ttf", "", 4/* remove bitmap */);