Yes, it is possible.
sv_user_t, delegation_t and proxy_signature_t can be used multiple times after having initialized them.
The same cannot be said for both sv_public_params_t and sv_private_params_t.
To avoid memory leaks, they should both be cleared before being used again.
All the data structures should be cleared when no longer needed.
The sv_user_t data structure is used to store the user's data.
It is initialized in a very lazy manner: while all elements are initialized when user_init() is called, their value is not updated.
This means that, if either of the user's keys are needed, the appropriate extract function must be called.
This becomes especially critical when passing the data structure to a function that will use the user's keys.
To enable the precomputation, the public_params_pp() function must be called after the public parameters have been initialized.
From that moment on, all functions that require the public parameters (nearly all functions in the library) will use the precomputed values instead of computing them on the fly.
This includes user_init().
Make sure to call public_params_pp() before initializing any user, otherwise the precomputation will not be used and the users will find themselves in an inconsistent state.