Beautiful job on your P39 - as usual.
Many of us would be interested in these techniques.
Thank you Russ!
When I apply microscopic decals, and yes you can read the text with magnification, I only put 2 or 3 in the water at a time. If you put too many in the water, after applying a couple the rest will be floating on the water! And that’s a recipe for frustration!
So 2 to 3 at a time because you don’t want them to separate from the backing while in the water.

Microscopic decals common at 1/72 scale!
After the decals soak about 30-45 seconds, I stab the edge of the backing of the decal, so always leave enough excess backing around the decal…

Now that you have the decal and backing on the end of your xacto blade, then carefully place near the final location on the model…

Then I use the end of a toothpick to slide the decal off the backing onto the model. Then I carefully slide into its final location with the xacto or toothpick. Then gently roll a q-tip over it to dry up all the water to fix it in place. Later I brush a little matte varnish over them.
Tips:
A microscopic decal will float on a drop of water, so dap the backing on a paper towel while on the end of the xacto blade prior to putting on the model. You don’t want it dry, but you don’t want a drop of water on the decal either. If you do end up putting it on the model and it’s floating on water, dap with a q-tip to wick up most of the water, and then slide into the final position and finish drying and pressing down by rolling the q-tip over it.
Also, should a decal end up separating from the backing prior to pulling out of the water, use your xacto blade to get it off the water. You have to gently place the blade near the decal and slowly raise it out of the water on the blade. Once it’s there, just slide it on the blade with a toothpick until 70 percent or more is hanging off the blade, then use the same method to slide off the blade with toothpick onto the model.
In conclusion…
It is really more of an exercise in patience than skill.

You need 3 hands, one for the model, and two for the xacto and toothpick…

…so I place the model where I can locate the decal without holding it. Once it’s transferred onto the model, then i pick up the model and slide the decal into its final position while holding the model.
Anyway, I hope I made that clear enough to be of use. Feel free to ask questions.