Hello,
I would like to create a folder icon with Fedora and Red Hat Logos. I have the following questions:
I use LibreOffice for the folder creation.
I saved the files in the ~/.local/share/icons/breeze/64x64 directory with the name folder-redhat.svg, folder-fedora.svg.

Now, the questions:

• Is it sufficient to just save the files in the ~/.local/share/icons/ directory, or I need to create the <themename>/64x64, <themename>/32x32...
• If I have to create all those directories, cut I simply use symlinks/hard links to the original file? I ask this because as far as I understand, SVG has no dimensions, so, I am confused by the need to create those directories.
• if I change my current theme (breeze), will the icons be available?
• So, if icons are bounded with the theme, how do I create theme-agnostic local icons?

While not familiar with all of the ins and outs of icon themes, I may be able to assist with a couple of things.
I believe the reason for having the separate sized folders is that it optimizes the common sizes that are most often used (it's quicker to display a raster file than a vector file as the vector file must first be rendered to a raster image) as well as allowing the theme designer to tweak the icon in different sizes (possibly providing separate sets of icons targeted for e.g. tool bar buttons vs. other places because they use different sizes in different places).

Doing a quick check of one of the themes I've got installed, I see that in the index.theme file, in the Icon Theme section, there's an Inherits key which lists out other themes that will be used as the fallback for that theme. So probably what you want to do would be to create a separate theme with just the icons you want to change/add and have it inherit from whatever base theme you want to use. Then when you want to change the base theme you will need to change the Inherits line in the index.theme file and reload the theme.