How much should I change my summary for each application?

Change a few words each time: the job title you are targeting, the two or three skills that match the advert, and the proof point that fits best. The basic structure can stay the same.

A quick routine:

• Replace the target role with the exact title from the advert.
• Swap in skills the advert stresses, if you genuinely have them.
• Choose the internship, project or job that matches this role best.

Example: For a finance role, "Accounting graduate with Excel and reconciliation skills"; for an audit role, "Accounting graduate with audit internship experience and attention to sampling and documentation." It takes five minutes and makes the whole resume feel targeted. Save each version with a clear name, such as "Summary - audit roles", so you can reuse it for similar adverts later.