@mage_goose use custom option import extension that helps you in adding custom options.
If you are looking for extension to add custom option and indicated both Magento 1 and 2, you may have a look at Mag Manager. It supports both versions and allows to copy-paste options from one products to another and import/export them that might be helpful for bulk custom options assignment.
I suggest you trying this magento 2 dynamic product options extension. The plugin allows to copy options or create and associate options templates to products. You can make changes in the template and all linked products will be updated automatically.
The extension allows to export or import custom options as well.
Hope it will be of help!