Disrupting a Good Tenant

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I have a somewhat easy, but worthwhile question. I have a tenant that has paid like clockwork since beginning a two year lease in March. In my lease agreement it requires the tenant to notify me of any adults that move in and they're required to get on the lease and pay another $100/month. I saw that this tenant got married in July, so naturally the spouse has to be living in my property but I wasn't notified. Would you mess with it, being that the tenant has been low maintenance and paid really well so far. Or would you send a letter notifying them that they need to add the spouse to the lease and pay up.

Please advise,