You can re-use a tenancy template you have found online for future tenants (providing it allows for the new details). However. it is important that you ensure that your template is not outdated. For example, it must not include cleaning fees or demand a deposit higher than 5 weeks' rent. You can read about what you need to check is no longer in your tenancy agreement.
Similarly, re-using the same template might also mean that certain clauses are missing from your agreement that are required to be there.
Aside from these issues. your are more likely to make mistakes in your contracts if you recycle your template!