[anon50118810]

Often when people talk about customizing applications, they mean rewriting your existing resume in a way that mirrors the job listing but without actually lying. Whether this is worth it or not depends on the situation, for example I understand this is really useful for U.S. federal jobs, but I don't think it's very useful for places where a recruiter skims resumes for basic fit and then passes them directly to a technical hiring manager. However it sounds like you were talking more about personal growth, which I misunderstood.

When you're unemployed and in the middle of a job search, you need to work with what you have, meaning you should make a resume that emphasizes your existing skills and apply to jobs that will value them. At the mid/senior-level no one will care much about any new skill you only know from a book or a Udemy course, so learning new skills is not a good use of time. At best you can hone your current skills, which might help in the interview but not with the resume, where the biggest drop-off happens.