Actually etching is damage and will show up NO MATTER how diluted the acid is. Even acid rain has a damaging effect on this type of tile.
See Saltillo Tile - ICT, Inc. for a FAQ sheet from a Saltillo manufacturer.
Otherwise you might end up with a problem similiar to this.
By the way, I know of no tile manufacturer that recommends muratic acid to remove grout haze or mortar remnants.
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