I want to create a custom attribute type that consists of 2 parts, a checkbox and an integer field. The integer field is to remain uneditable unless the checkbox is ticked.

Is this possible to do ?

Maybe you could have 2 fields a Boolean type (checkbox) and a simple text fox (for the integer).
Then you could create a custom Pre-Condition, called here Operation Advisor that could set a rule that the text box is available only if the boolean type variable is true.

Now, to create a new custom Operation Advisor I cant help you so much...
Because I'm trying to figured out how to create a new one.
There is a article in the library(jazz.net library) https://jazz.net/library/article/495 that guides trough the phases to create a new one.
But it does not say where do you get the code or things like that!
Hope we could be helped from this post