I have trouble understanding what you're asking. The 100/300 statement doesn't ring any bells at all, as the closest thing I can think of is the world gen mineral scarcity, which typically has a much higher value, so that's probably not what you refer to.
Also, I'm unsure about which meaning of "regenerated" you refer to, i.e. "restore mined minerals" (which the script does not support, but I think there's a fortress mode DFHack script to refill veins), or "generate the composition from scratch", which it doesn't do automatically, as all manipulation is manual, so each change made is manual.
The functionality supported is to modify existing geo biomes and to build new ones in a manual process.
- You can expand or shrink the thickness of layers in the geo biome you're working on (one geo biome at a time).
- You can morph the layer material to any other layer material. This wipes the vein/cluster inclusions clean, so you'd have to repopulate those manually (as desired).
- You can add and remove veins, clusters, and inclusions in veins and clusters. Removing a vein/cluster will also wipe their inclusion sheet clean.
- The selections of veins, clusters, and inclusions respect the rules laid out by the raws, so you can only add vein/clusters/inclusions where they're allowed (you can't add any of those to soil, for instance).
- I've been unable to find the criteria for when a layer is "alluvial", so things that should be possible in alluvial environments cannot be added (and I think that completely excludes some gems that would otherwise be found in soil layers).
- The script doesn't restrict where you place your layers (so you can create a sand layer deep down, for instance).
- DF seems to always generate 4 Z levels of soil (possibly 3 in deserts) in the geo biome. However, the DF logic supports up to 10 at the top. Each 5 Z levels of elevation above 100 reduces the number of layers by 1, "eroding" the top ones first, with some bugginess involved when layers are multiple Z levels deep. This means that an elevation of 141 and above will not get any soil aquifer, as aquifers appear at the 3:rd layer or below (you can still get stone aquifers).
- DF supports a maximum of 16 layers (anything beyond that is simply ignored), and the script enforces the 16 layer limit.
- The geo biome describes the layer stack, but it does not guarantee the whole stack will be present at an embark, as the SMR will cut off the parts of the geo biome that would have appeared deeper. This can cause DF to report the presence of flux or deep metals for an embark when those are actually cut away by the SMR (similarly, DF can report the presence of clay and aquifers when soil erosion causes those to actually not be present).
- I think the lowest geo biome level is extended downwards as needed to ensure there is something all the way down to the SMR if the geo biome's vertical extent is lacking.