Is there a proven technique for removing grout joints without chipping porcelain tiles?
There is a Dremel Grout removal attachment, which consists of a fixture to hold the tool at a 45 degree angle, and you can get a 1/16 inch carbide cutter bit.

I've used this setup several times to remove grout for renewal or tile replacement.   It can work quite well if the grout is really a sixteenth wide.  Its not easy, but you can chip the tiles if you're not careful.   I inevitably break the bit, and will always buy at least two.

https://www.dremel.com/en_US/products/-/show-product/accessories/568-grout-removal-attachment