How long does PowerPoint maintain your customization options?

until you close all presentations

until you update your Windows settings

until you close all programs and log out

until your installation ends or you make changes

PowerPoint maintains your customization options until you close all presentations.

Explanation:

You  are able to customize from your potions on a power point until you have your presentation opened in front of you. as soon as you close them, after the warning for saving it for which you can save changes to the file, then you will not be able to customize the file in the read only mode.

You can alter the file after saving changes however, as the documents remain editable for as long as you want to keep them but they are only customized on the edit mode for convenience.