I’m not part of the support team, but I think something like this can quite easily (“easy” depending on how well you know this stuff, of course) be done by setting up custom fields with ACF and Pro’s Layout Builder.
You would add two new headline elements next to your product price element. One could say “incl. 0% VAT” and the other “incl. 25% VAT” or whatever you want.
Since doing that will simply show two new headlines simultaneously, you’ll want to set up conditions so that the headlines only show whenever they need to be shown.
So you could create a “True/False” custom field in ACF and display it on the product page’s backend. The “True/False” field will show up as a simple checkbox toggle, which you could name “Second-hand product?” for example. You’d then tick that new toggle on all products that are second-hand.
(You can reverse the logic, of course, if you have more non-second-hand than regular products since you probably want to tick as few checkboxes as possible.)
Next, you would add a condition to the headline element that says “25% VAT” and tell it only to show whenever that new checkbox is not toggled. This would also make it the default since, by default, the custom checkbox won’t be toggled, so all products would automatically show that they include 25% VAT. You’d add the opposite condition for the “0% VAT” headline. So you’d tell it to show whenever the custom checkbox is toggled.
What you’re essentially doing is this:
If second-hand checkbox is ticked, show headline 0% VAT .
If second-hand checkbox is not ticked, show headline 25% VAT .
The condition type you’d add would be a string condition.
So the condition for the 25% VAT element would be:
{{dc:post:meta key=“second-hand_product”}} [is] 0 <- 0 meaning the checkbox is not checked.
And for the 0% VAT element would be:
{{dc:post:meta key=“second-hand_product”}} [is] 1 <- 1 meaning the checkbox is checked.
Doing it this way would also ensure that both headlines never show at the same time since they can’t be checked and unchecked at the same time.
There are of course countless other ways you could achieve this. If you have hundreds of products and ticking a newly added checkbox on all of them would be a pain, you could set up a category-based condition. So if a product is in category x, show the 0% headline. If a product is not in category x, show the 25% headline.
Since I do a lot of this stuff with conditions on my site I thought I’d quickly chime in and try to help, but I just realized that my giant explanation here might be more confusing than helpful. Sorry if that’s the case 
