(1) I was able to set Tax Type = Python Code:

import datetime
time_of_change = datetime.date(2015,1,1)
today = datetime.date.today()
if today < time_of_change:
    result = price_unit * 0.14
else:
    result = price_unit * 0.15

(2) I found the community model account_chart_update for v7.0 that updates taxes++ based on the templates.