For any of these lenses, "framing" really doesn't get at the issue - the issue is getting the right magnification and the right working distance. In truth, the word "magnification" is the exact same thing as "framing" in this case, except that magnification suggests what is really happening, whereas talking about "framing" allows people to think in terms of a zoom lens.
The reason for this thinking is obvious: The draw of a zoom lens is that you can better control depth of field and you don't need to walk very far to change your framing. At macro distances, depth of field will always be very limited no matter the lens (most people usually find themselves trying to increase it, not decrease), and working distances will be so small that the effect of a zoom lens of getting "closer" (magnifying) a distant subject is usually not the concern - instead you are trying to get farther away. In both these cases, it seems that a zoom lens would actually be more of a liability than the simplicity of changing your magnification only by moving the lens back and forth, and focusing.
For slight changes in magnification, yes. But a fixed focal length macro lens cannot change magnification 3-fold or more, as in coin vs. lighter. That's going to require moving the camera - re-framing the shot.
RE: the 135/2 vs the TS-E 90, the 135L achieves 0.19x native and 0.41x with a 25mm extension tube; the TS-E 90 has a much closer MFD and achieves 0.29x native and 0.60x with a 25mm tube.
RE: DoF, that's the main challenge, IMO. With a coin or other object well-represented in 2D (as Mt. Spokane's shot nicely shows), DoF isn't an issue. But with a 3D object like many small products the OP will likely want to shoot, DoF may be a limiting factor. With a macro lens or a telephoto like the 135L, that means soft images at f/22-32 or focus stacking. Or, a TS-E lens where the tilt allows control over DoF.