Aging will do it, as well as heat and pressure. I personally do a "wet toast" (in a pressure sealed container so it doesn't dry the tobacco; left vs. right, toasted) at 140°C. In fact I'm doing another round today. My understanding is that in the case of brown flake, a bright and lemon Virginia flake is heat-pressed. View attachment 79877
Absolutely fun! Once you go down that road there's no looking back. The blending tobaccos sold by most of the major manufacturers are, in most cases, the absolute cheapest and lowest-quality leaf they have. It's garbage compared to the quality of tobacco that you strip and shred yourself. I'm sure there has to be bad whole leaf out there somewhere but I've never had it.
Of course you have to be honest with yourself. There are some trials that end up in the garbage. But on average I think approximately 80% of my whole leaf experiments are great--not mediocre, but great. I'd say that my trials with store-bought blending leaf yielded a "passable" smoking mixture maybe 10% and the rest was unsmokable garbage.
One interesting thing, though, is that it's very labor intensive. You couldn't possibly go into business selling sui generis tobacco mixtures without the proper equipment.
Here's my process for Virginia cut plug, which is my base for many blends.