Button text that changes depending on previous actions (pay now vs. update order)

Question

The essence of my question is this: is it problematic to change text of a call-to-action button based on user input to a form?

More specifically: we have a short form within a dialog that allows users to change a subscription (e.g., add or remove data from their plan). Some changes will apply immediately and thus charge immediately, and some changes will be applied later. We do not expect users to encounter this dialog often.

The flow is this:

1. The user makes changes to the plan
2. On blur from each change:
   1. If the change would incur charges, we add/update a line in our summary section that says "Amount you will be charged right now: $xxx.xx"
   2. If the change would instead change a future payment amount (e.g., they've reduced their data), we add/update a line that says "New monthly payment (effective 8/1/2015): $xxx.xx"
3. Below the summary, they can either click the confirmation button or cancellation button.

We want to make sure it is clear that clicking this button will immediately incur charges in some cases, without seeming out of place/worrying customers when no charges will be incurred.

At this point, I see three options:

1. Pick a phrase that encompasses both purposes
2. Make the button text conditional on what will happen.
3. Have a separate confirmation + summary page

I'm having difficulty coming up with a phrase that encompasses both cases without dropping the emphasis that you will be charged immediately, so I think that option is out. The team I'm working with would prefer it to all be on one page, which is why I am less open to that idea, but if the text of the button changing is confusing, we may go the route of a separate page.

Answer 1

There's two ways you could go about this:

1. If users must configure payments at this step, then your button could read Configure Payment or Choose Payment Option.

2. Since changing subscriptions and setting up payments are multi-part steps, it may be best to break the process into two steps. Save and Continue then Save or Submit Payment on the next screen might make the process more clear.