What would a fitting colloquially accepted translation of the word takana be? Assuming we are dealing of course with a rabbinic decree and so as to convey the intent as apposed to 'gzeira', 'syag', 'mishmeres' and such.
If you want to specifically distinguish, I would go with corrective:
something that corrects or counteracts something undesirable
The Rabbis established a corrective. Bishul Yisroel is a Rabbinic corrective against intermarriage.
But with the caveat that from my observation the distinction between takkana and gezeira is not regarded as important in many places and thus would really not necessarily lead to a better quality translation to translate them differently based on the original word choice.