Re: Help with DIY shirt bleaching.
Hmmm... I'm not sure.
Perhaps you could do multiple treatments, washing inbetween them. That would control the location of the bleaching, and maybe stop the chemicals eating through the fabric.
Also you could use oxygen bleach like nappy sanitizer instead of chlorine bleach. I happen to know that it's also effective, after accidentally leaving it and dry clothes in the machine too long before washing.
It left me with a white constellation on some clothes which was really cool (and orange bits on others which wasn't really - but could be if you like orange or the whole industrial safety gear vibe), but too long damages fabric so you get holes fast on those bits when you wash. It does look good to have the little holes with pale seared edges, but it might not be your thing.
If I were you; I'd try mixing Napisan to a thin paste and brush it onto damp/dry clothing, leave for ten mins then wash. Or sprinkle dry Napisan powder onto damp clothes in your pattern for ten minutes.
Easier to control and less seepage, then you can repeat it to get more effect where it needs it. The first go will probably get it down to the orangey pigments then another might remove the colour.
Also consider using masking tape to block off bits you don't want affected, that will reduce the chemicals seeping under it. Or even wax.
Ps. Laundry powder is an alkaline - so if you want to stop at the point where it looks good or before the fabric is trashed, washing it in laundry detergent will neutralize the acidic bleach and stop the process. Baking soda could work too, just wash and rinse well for both to remove bleach traces.