I am wondering if I can change the format of a single character within TEXT.
I know that you are able to change the format of a single character
within MTEXT. This is the string code that appears in the properties
box for MTEXT. {\fCode2000|b0|i0|c0|p2;\u+23DA}
I am trying to use Unicode 23DA which is an electrical earth symbol in TrueFont type Code2000.
Are we able to change the TextStyle of a few characters like we can for %%uUnderline%%u?

No, this is possible only in MText.