John is a pig. <Present>
John was a pig. <Past>
To use were, you'll need if, a hypothetical:
If John were a pig, ... .
...., as if John were her pet.
He always follows her around as if he were her pet, (but he isn't a pet).
Change the verb to was and the meaning changes:
He always follows her around as if he(truly) was her pet.
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