Don't do undeclared mods. Not worth it, at all. Any excuse to not pay out and they will jump on it. Have you actually inquired to see how much the mods you plan would actually increase the premium? You might be pleasantly surprised. No harm in asking anyway, then you can make a more informed choice. Also, 1 year driving experience (named driver) hardly changed my premium at all, certainly not a deal breaker. So it is worth shopping around and stating 0 years ncd.
Remember to put plenty of experienced drivers as named drivers, has a huge impact.