I am installing a tile floor, and it will meet up to a carpet in the family room. There is about 25' long stretch where they will meet. The carpet has an aluminum retainer and I had intended to stop the tile about 3/4" short of the tile, and install a wood transition over it, so that's where I stopped the hardie backer. Now I want to install an aluminum edging strip and need to extend the hardibacker about 1/2". Is there something I can do to extend the backer without tearing it up and starting over? Can I make a form and pack it with grout or thinset? Picture attached. Tile is just setting in place.