I think it will depend heavily on which plastic and legend it is. Different dyes might bleach or dissolve differently. In the case of clacks I am sure he has changed the composition to improve it over time. The translucent ones are probably a very different plastic for example. That said, I think the risks are low with denture tabs and if you want you can take a small swab on the inside of the cap and see if you affect the plastic at all, and if it does, you haven't completely destroyed it.