Personal recommendation to not cause huge reflected HT voltages back into the ignition modules, commensurate with that is the quality of the ignition coil construction. high leakage inductance ( coupling between primary and secondary windings ) such as the bosch GT40 open frame model, will nuke a box at some stage, why bosch brought out the "electronic ignition" variant of GT40. Rubbish coil no matter the PR blurb. The GT40 is points only coil, the capacitor ( quaint term "condenser" as in condenses electricity ) across the points damps much of the extraneous reflected voltage waves. The only time i suffered a nuked iis was on a Duck S2 Millie with pair of GT40's. Toughened up the protection on the drive transistors, no failures subsequently again, on any iis module.
While you may not effect the ignitech, Red, you will have significant high voltages developed internally of the ignition coil, stressing the interwinding insulation. If lucky no problem, if unlucky the reliability is impinged by repeated high voltage standing waves. The odd time maybe ok, as a part of workshop practice, would not recommend oc'ing the HT leads.
Possibly some of you may have seen a spark from an open HT cover to engine block, that requires well over 35KV, sparkgap bridging potential takes 3KV per mm at sea level. 10m/m would need 30KV, 20mm 60KV to ionize a gap that size.
Each owners call of course, good practice takes only a few minutes, HTH j.
