For instance, I want an ampersand in D&D, but it gets filtered out.
Unfortunately, this is not possible.
From the Ask Question page, the only allowed characters for tags are: a-z, 0-9, +, #, -, .
However, I do have a solution:
The latter will ensure that anyone who tried to type 'd&d' in the box will have the proper tag put on the question. This works because the ampersand is silently stripped from the input, resulting in an actual input of