Add ons after booking

Is there a way to send an email to a guest prior to their stay to remind them about optional add ons, like pool heat and beach service that includes a link to purchase? I have a template email but I would like a place for them to click to add these services and pay right there. 

Unfortunately, at present, no, this is not possible.  If you are using tags to denote when optional add-ons have or have not been purchased, then you can use those as criteria on your triggers to send or not send a reminder - but the actual purchasing requires manual changes to the charges by you.