This question is in reference to Atlassian Documentation: Associating screen and issue operation mappings with an issue type
An issue type is a defining characteristic of an issue, not some arbitrary attribute. To see how much sense it makes, try changing the words to something more abstract. "I have added type as "Dog" I would like to add another issue type in the same ticket as "Cat"". You want to add your cat to your dog?
I think what you really mean is that you would like to add related issues. The most simple and clear option is probably sub-tasks. Create a "Requirement" and then have a sub-task type of "new feature" you can add beneath them.
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