In the Geometry ribbon there is a button to copy vertical geometry.

There is an option to Copy Projected:

When used, it does project the vertical intersection points of the source profile to the target horizontal, perpendicular to the target alignment.
In the following picture you can see CL2 profile projected onto CL1.
GeomBL1 and GeomBL2 are controlled points used for CL2 Vertical Intersection Points  to highlight how it is being done.
You can see how GeomBL1 and GeomBL2 are also location of projected profile on CL1.

It means that slopes can be changed even if horizontals are parallel.
Note that if you don't use Projected, the source profile is copied to the destination alignment start to start.

If you want to create the vertical of a parallel track so that you have exact same elevations, then you must use Project Profile to Element.
However, you will get a linestring and not geometry made of slopes and curves.

If you want to have a geometry made of slopes and curves on parallel track, then it can't be always 100% accurate because cumulative distances are not the same on both alignments.
In this case, you can create the exact same profile only along straights, then you have to fill the gaps.