Is it more effective to add yeast before or after kneading?

The whole idea of adding the yeast before kneading is to be able to mix it uniformly. By adding the yeast after the dough is formed, it will be mechanically more difficult to combine it and you might end up with lumps of yeastless dough. Those lumps won't rise.

I suspect your bread will have a denser, non uniform crumb.

I've seen/used a lot of bread recipes, but never even heard of one where the yeast was added after kneading. You'd think there'd be good reasons for that. Kneading actually has a double function: not just releasing gluten but also mixing, so why try to separate them?

Luciano is certainely right about the unformity of the texture. I believe the texture of gluten would keep ingredients from migrating and make mixing more difficult, which would be catastrophic for yeast. In fact, if you add some discrete chunks of something to the bread you usually add them after kneading or at the very end (olives, bacon bits...), but all ingredients that have to be mixed in uniformly (salt, spices) get added before kneading.

There are even recipes that separate out the initial rising of the yeast from the mixing. I learned at first from the Tassajara Bread Book, which generally uses a sponge method where you allow liquid, yeast and a small bit of flour to start fermenting before adding other ingredients (especially salt). I've often transposed this method into other recipes as I find that does give a good texture and a better rise.

If you add yeast after you develop the gluten you will have to knead a lot to make sure it is distributed throughout, and you will end up overkneading your dough leading to a tough result.

Kneading is only one thing that develops gluten, yeast assists in gluten development by opening up the structure when it releases CO2. Opening up the structure allows the enzymes, water and gluten proteins to move more freely and form connections. There are no-knead techniques that develop great gluten structure. Adding yeast after kneading has loads of downsides but no upside.

The method i use follows this concept and works for me. My favorite recipe is for a baguette dough where the first step is to mix (mix well, no kneading) only flour with 50% of its weight of water and let it sit, covered, for 45 to 60 minutes. After that, add 10% of the flour weight of water plus yeast plus salt to reach 60% of water. Mixing it is messy, but works. Leave it covered for another 45 to 60 minutes.

Then knead it lightly, for 5 minutes. Cover again and wait 45 minutes. Here you can put in the fridge for 24h to make a tastier dough.

Or form and strike the baguette, leave it covered for last 45 minutes and bake (hot oven, small ice cubes dropped in the bottom of the oven). Always work.