I just had a similar question. I wanted to paste text from one graphic to another (A to B), but keep the text formatting and style of the receiving graphic (B). Reading Neil's post below gave me the idea to paste the text into TextEdit (on a Mac) and then copy and paste it into the B graphic. Which worked.
I also noticed that when you are creating a new text graphic, it will use whatever text style was selected last.
So if you create a "plain text" graphic, then copy the text from your text source, paste it into a TextEdit (or equivalent app). Copy the same text again. Then in PP select the plain text graphic, paste your text into a new text graphic (or even into the plain text graphic) and it should take the properties of the plain text graphic.
You can save the plain text graphic as a graphic preset to reuse it whenever you need to clear the text formatting.
I hope that helps and makes sense. If not let me know.