Electrical – Smd footprint Altium

I suspect that the reason for the different footprints is to allow for the different heights of different parts.

For example, a SMT ceramic capacitor is typically about as tall as it is wide. While a "typical" 0402 resistor I just looked up (here) is 0.5 mm wide, but only 0.35 mm tall.

Because the capacitor is taller, it needs a longer "toe" in its footprint to allow a good solder fillet to form (I haven't checked if this is actually what's different between Altium's resistor and capacitor footprints).

Altium's footprints are just a reasonable guess at good footprints for typical parts in each category (resistor, capacitor, inductor). To really optimize your design for high manufacturing yield, you should consider the actual height of each part number in your design, and account for your manufacturing process: for example, reflow and wave soldering have slightly different requirements for optimum pad sizes.

Hopefully I understood what you are trying to do.

You have to create a mechanical pair.

With a PCB open click Design Board Layers and Colors (Shortcut: L)

In the bottom left corner, you'll see a Layer Pairs Button. Click it.

Add your layer pairs together (like Mechanical 14 and Mechanical 30).

That's it.

Now when you switch components between layers, the items on the mechanical 14 will switch to mechanical 30 and vice versa.

I'll try and add some images and format this answer to be a bit more clear later on.