浸了 75% 酒精的草藥後, 是否仍然75%?

原則上應該是。
不過，如果藥草內容與酒精產生化學仍用，
則可能有異常反應，如增減濃度。
順帶一提，７５％的酒精，大概是消毒火酒來的吧？

I think it will be diluted due to the subsistance extracted from the herbs. Also, alcohol with such concentration would absorb water.

浸了 75% 酒精的草藥後, 是仍然75%!