The answer to your question is dire: beyond trivial replacements (where manufacturers guarantee compatibility, or it's just minor packaging differences), replacing components is design. A different person can do this work, but only if they are up to the task of designing such circuit. Yes, in practice this work is looking at datasheets and doing Spice simulations, among other things.
It's best done by the original designer. Because they know their design, it's least work and least surprises.
If the designer has always worked with the premise they can just specify any component and purchasing department will get it, then this process must change. Co-operation between designers/purchasers, and fast actions are important now. Also some risk-taking; you need to order what you can get and make those parts work.