Is it possible to dictate a UV map instead of pulling one? I have experience making textures for items that already have a UV map, but this is my first try making one myself. I apologize for not being able to more precisely describe what I want to do; I suspect that not knowing the terms is hampering my google searches in an attempt to find the answer on my own.

I have this model, made in SketchUp, shown with textures:
https://gyazo.com/f6585ce8948666f694c8abd05701e609

When I unwrapped it or otherwise had Blender make the UV map, it created a lot of non-overlapping rectangles, one for each face. However, I liberally re-used textures when making the lantern, so that was not at all an efficient use of the available space. So, I made a texture map by hand that is much more optimized The problem is, I am not seeing a way to tell Blender which areas to use on which faces of the model, and all the tutorials and the like I am finding are trying to help people with more conventional starter tasks, like upholstering a chair or making a shirt, where what I want to do would be insanely fiddly.

Is there a way that I am missing to tell Blender the intersections for the UV map, or am I doomed to having it tell me? I am aware that in many situations this is precisely backwards, but for this project, it would be a great boon to my final file weight and texture quality. I am willing to use programs other than Blender if it turns out this is a thing you need Program X for.
In Edit mode, select the face you want to manually set the UV map for and select Mesh/UV Unwrap.../Reset from them menu (or press U and select Reset). This will reset that face to cover the whole UV space. Then in the UV Editor window (while the face is still selected in the 3D viee) you can manipulate the UV mapping as desired (select the vertices (or A for all) and use G, R, S for Grab, Rotate, Scale, etc