Cost of loading manually modified instances at runtime, on mobiles?

Questions & Answers
1

As a general rule for mobile development, is there any significant in-app drawcall or CPU negative consequence in using manually modified multiple instances of a unique prefab instead of saving all these instances in their vanilla form (that is, pure copies of the prefab)?

For example, when building a place for a game, like a town, if I place 50 instances of the same prefab in my scene, will they significantly require less computation if I don’t change any of their parameters (the overriding thing that shows some fields in bold)?
Said manually and specific modified paramters could be anything like some having a smaller collider, some pointing to a different texture, some made heavier, etc., so in the end they all have something unique.

What is the kind of penalty to expect there and what are the extreme cases to avoid?

PS: with AlwaysSunny’s answer, I realize this question lacks one detail.
The obvious consequence of not modifying instances of one unique prefab is that it forces developers and scene builders to use different prefabs, one for each different case.
The project logically and rapidly grows in size then.
However, if storage size isn’t a problem, it’s still important to consider the effect of loading variants of a unique prefab vs loading several prefabs, each covering every single different case.

2

Your “placed and modified instances” approach is superior to the “prefab for every flavor” alternative for a litany of reasons.

Chief among these are your convenience, and the memory footprint of the game on both disk and ram.

Any performance differentials in other areas are going to be negligible, provided the million-and-one other relevant considerations are addressed with a similar degree of attention to optimization.

Draw calls will be unaffected, except in those situations which prevent batching for normal reasons. CPU and other loads will be largely unaffected.

Unless somehow the every-flavor strategy is beneficial for your convenience, stick with what you’ve got.