Hi hannaro,
If you're welding to D1.1, in Section 5 Fabrication, 5.15.2 states that machining, thermal cutting, gouging, chipping, or grinding may be used for joint preparation, or the removal of unacceptacle work or metal, except that oxygen gouging shall not be used on steels that are ordered as quenched and tempered or normalized, because of the high heat input of the process.
Any altering of the HAZ during rewelding would probably depend on the base metal, the welding process, the welding procedure, and the extent of the repair, which you indicated was a little over 3/8" deep in a base material which is a little more than 3/4" thick, if my conversions are correct. I can tell you that as far as gouging goes, from a metallurgical standpoint, the chemical changes which occur with carbon arc gouging may produce a thin hardened zone in some metals, but subsequent welding remelts this zone and reduces the hardness.