The phrase "already a practice" is correct and usable in written English.
It can be used to indicate that something is currently established or commonly done.
Example: "Mindfulness meditation is already a practice in many workplaces to enhance employee well-being."
Alternatives: "already a norm" or "already a routine".
Putting on Acts I and II under the rubric "The Fall of Troy" was already a practice during his lifetime.
He requested that he be allowed to order them killed on the spot when captured in arms (already a practice among many Union units).
Scientists and engineers suggest an interim fix is to store more spent fuel in dry casks, already a practice at many plants, although moving them to a remote central site would be better.
This is already a practice in some European countries, where laws requiring blood ties to existing citizens have been relaxed to give birthright citizenship to children of illegal immigrants who have lived in the country for some time — Britain, for example, requires 10 years and no long absences from the country.
If you already have a practice, you might examine how to incorporate this idea of harvesting the light as we begin our trek toward the winter.
Health care providers are important prompters of syphilis testing and many MSM already have a practice of routine testing.
It is already a common practice for nurses who work at hospitals or for doctors in private practice to transcribe and transmit such prescriptions.
Tertullian seems to have been the first to object to infant baptism, suggesting that by the 2nd century it was already a common practice.
Among their duties will be ensuring male and female guests do not mix in the same rooms – already a standard practice in most Afghan weddings – and that the bride is modestly attired.
And fast-food restaurants can advertise "free refills" - already a common practice in American restaurants - and charge more up front.
