Yes, it is possible to create your own UV mapping, not simply a surface. You still don't understand it, but if you insist, please allow me to explain it again. Or you may simply disregard the following.
The geometry tool and the geometry shell are not the same thing.
In brief, anatomy tools such as Golden Palace, Dicktactor, and Wet and Tanned Body all employ geometry shell. They do not use the geometry tool to create a new surface from the same UV map. It is not user-friendly. And it has no chance against laying another layer on top.
The Geometry Tool, also known as the Gemetry Editor, is a tool used to modify the polygons and vertices of an object. I read the above link a long time ago. In the first link, they use the geometry tool to choose a portion of an object and then generate a surface from that selection. When you leave the DAZ Studio, you can do a lot more. I've been considering uploading it for a long time. Once I've updated my game, I'll include instructions on how to unwrap UV and create entirely new material zones.
Yes, getting what you want is the most essential thing. But...
Assume you wish to place the raindrop and steam structure on a polished surface. Because the table is bright, it must already contain some roughness maps. Metallic, glossy, dual lobe, top coat, and so on are some examples. Your prior roughness maps will be lost if you replace the rain texture on your table. You can attempt adding LIE, but you will be severely constrained in terms of functionality compared to what Geometry shell can do.
Since you mentioned customizing, you can't just rotate on a surface with two polygon directions determined by UV mapping. Occasionally it will appear fine, and sometimes it will not. So you might want to learn how to make a fresh UV map. That's why people utilize 3D painting tools such as Adobe Substance Painter. You don't have to worry about UV direction while using these programs since what you see is what you get. If the UV map is simple enough, photo editing tools such as Photoshop may be used to follow the uv direction.
For example, if you rotate the map in one way but your shirt has one direction for arms and one direction for body, as you previously stated, you will need to design your own surface and rotate the surfaces accordingly. When you have a complicated item, this will take a long time. In this case, employing 3d painter or carefully painting in photo editors while following the orientation of the UV map is the best option. Because geometry shell cannot generalize all objects, specialized products such as Golden Palace for GENESIS 8 FEMALE exist. GENESIS 8 Male's wet and tanned body. Because various UV maps need the use of different custom geometry shells. In these circumstances, neither your strategy nor mine are user-friendly or ideal.