http://judy-volker.com/Hometowns/Potsdam/Garn...
http://judy-volker.com/Hometowns/Potsdam/Garr...
"Always be Faithful and True"

... immer noch: "Üb' immer Treu und Redlichkeit!" . . .

... i.S.v. Übe dich immer in Treue und Redlichkeit . . .

... mit: to practice AE / practise BE = üben | übte, geübt |

... besser ? . . .

Und wie wär´s mit der 2. Zeile?

... und wie weit kommst du selber damit ? . . .

http://motlc.wiesenthal.com/site/pp.asp?c=gvK...
... The bells of its carillon punctuated every half hour with the melancholy song set to a Mozart melody: "Always practice loyalty and honesty to the coolness of your grave" (Ueb immer Treu und Redlichkeit . . . ). ...

If the question is whether there is a standard translation, then no, there probably isn't. You could translate it more literally, or try to reproduce the meter, e.g.,

Forever true and honest be,
until thine early grave.

That's not very good, but it at least keeps the 'früh' part, which might be useful in reference to Mozart.

The translation with 'coolness' seems to have chosen the U/Ü vowel over the literal meaning, perhaps for a text to be sung.

... next to being demanding (#3), the OP has been sloppy twice in copying the lines . . .

The Wiki-article which he linked to clearly states:

„Üb' immer Treu und Redlichkeit
Bis an dein kühles Grab" . . .

Hmpf, after all that trouble I went to to get 'early' in there.

Be loyal, practice honesty
until thine own cool grave.

But that doesn't come across very well for modern readers, who will think, What's so cool about a grave? Until the cool of th'grave? Also not so hot.

Never mind ...

... read 'kühl' like 'cold' . . .

LEO has: grave-like cold = die Grabeskälte . . .

PS: ... and don't blame me . . .