Every now and then, a customer will ask to install a tinted window film over a layer of safety and security film. We don't recommend this procedure for several reasons. First, the adhesive bond is not the same when applied to another piece of film compared to glass. This means there's a chance the second tinted layer could become detached from the original film. Another reason is the thickness of the films highlights any contamination that might exist. This could create a less than professional looking installation and a less than satisfied customer. Finally, Johnson Window Films will not warranty any film applied to another film, so both you and the customer would be taking a big risk.
Instead, another option is to suggest one of Johnson Window Films' tinted safety and security films (basically a tinted film laminated to a security film). This will improve your chance for a successful installation while maintaining the JWF warranty coverage.
If the customer insists on installing one film over another, make sure you are very clear that the film will not be covered by any warranty guarantee due to the potential product issues that exist. It's important the customer understands the risks of applying two pieces of film over the same window.