This page discusses which advantages could feasibly be gained after character generation. Please note that for the time being I have listed only advantages from the Basic Set and not many from the Compendium I (or any other source). I'll add more later as I get time and suggestions from other people. The entire contents of this page is subject to debate.
These advantages could feasibly be purchased after character generation with earned character points. For many of these, the book expressly allows bying it, or it is a non-intrinsic advantage that anyone could feasibly obtain. Some special adventure might be required to explain gaining some of these.
You might be able to get these advantages after character generation, but I'm not sure. It might require a special adventure that can justify it (i.e. training in the Ninja Secret Camp). Alternatively, the GM might rule that they can be purchased but at double the book cost. These are very much subject to debate.
These are advantages that could be obtained but require a tech level in the gameworld that is high enough to have cyberware, bioware, or enhanced vat-grown clone replacements. There might be a way to obtain these at lower tech levels via magic or someone highly trained in the 'Weird Science' skill, but this is really iffy.
This is a list of advantages that a character could temporarily or conditionally aquire, provided they are wearing some magic object, be it a ring, amulet, belt, hat, or whatever. This is by no means an exhaustive list, just a list of ideas that fit the common, literary understanding of storybook magic.