Wikipedia:Template editor

The template editor user right allows trusted coders to edit templates and modules that have been protected with the "protected template" protection level (usually due to a high transclusion count). It also allows those editors to edit editnotices for all pages, not just those in their own user and talk pages.

There are currently template editors and administrators (1,417 total).

Editors are permitted to exercise this permission to perform maintenance, answer reasonable edit requests, and make any other simple and generally uncontroversial edits to templates, modules, and editnotices. They are also permitted to enact more complex or controversial edits after those edits are first made to a test sandbox, their technical reliability and their consensus among other informed editors having already been established.

If you have the template editor user right, please ensure you have a strong password and follow appropriate personal security practices. Because a single rogue edit on a highly visible template could affect at least one million pages, a compromised account will be blocked and its privileges removed on grounds of site security. In the unlikely event that your account is compromised, notify an administrator immediately, so that they can block your account and remove any sensitive privileges to prevent damage.

The key to wisely editing templates is to thoroughly test your changes before implementing them. Each template has a default testcases subpage which should be used for this purpose. It is important to test whether your changes have introduced any errors or not, which can be easy to spot if test cases are well-set up.

Expect to be held accountable for all changes you make. Be receptive to any concerns or complaints that others raise.

Repeated failure to adhere to these restrictions can result in revocation of permissions. If the failure is particularly egregious, any administrator reserves the right to remove your template-editing access summarily and without warning, even for a first offense.

...
Wikipedia