Recently the client has added another requirement which adds a good 5-15% time overhead per small project that I'm undertaking and I'm wondering if it would be worth it to ask for a raise, or would that be taken as crass/naive as (I said before) I'm relatively inexperienced and making extremely good money all things considered. Am I being selfish?
If the client adds an additional 10% requirements to the job and you do not adjust your billing then the client is reducing your pay rate. Upping your bill to reflect the new requirements of the job is not giving yourself a raise.
If you don't want to renegotiate the contract then you can still bill for the project as spec and then by the hour for deviations from spec.