In practice, no—you generally can’t turn a 50mm lens into a 35mm lens just by changing element spacing and still expect it to focus well. Vintage lenses were carefully optimized, and even small internal spacing changes usually hurt sharpness and introduce aberrations. On many simple 4-element designs, focusing is done by moving the whole optical unit together, not by changing internal element spacing.

Moving the lens closer to the sensor changes where it focuses, but it does not correctly redesign the lens into a shorter focal length. That’s why focus breaks, especially at infinity.

The proper tool for this is a focal reducer (also called a telecompressor or speed booster). It adds optics between the lens and camera to reduce the effective focal length and give a wider angle of view on APS-C, while preserving normal focusing behavior far better than modifying the lens itself.

Some lens-specific hacks exist, but they are exceptions and usually reduce image quality. So the practical answer is: don’t alter the internal lens spacing unless you’re experimenting and accept worse results; use a focal reducer or buy a wider lens instead.