You'd be better off putting the new 12-inch numbers
above the current stripes - in my opinion.
It is a pet peeve of mine that so many "artistic" paint shop embellish N-numbers and IMPO (and that of my FAA PMI) render them invalid per the regs in Part 45.
I see a lot of what I consider to be invalid N-numbers - and I collect photos of them. Most recently the trend has been toward those painted the exact same color as the background with only a contrasting outline - that is not legal per the regs.
By definition the N-number must be of a
contrasting color to its background and similarly the actual N-number must be comprised of
continuous characters - so by that criteria only the solid interior portion of the character is the actual number or letter and the outline constitutes nothing more than
ornamentation -which too must be minimized.
It used to be that people (paint shops etc.) were more careful to interrupt stripes around the N-number but apparently no more. Stripes of the same color(s) as the N-number penetrating or carrying through the N-number itself to me also constitute improper or illegal ornamentation.
There is an AC that describes a rule of thumb - a 12-inch N-number must be clearly legible from 500 feet away. Ref. AC 45-2C (or later revision if applicable) Section 8, paragraph (c) in particular.
Also, the regs specify height vs. width and spacing ratios, which many alternate fonts do not satisfy. It's not "rocket science" but yet so many people still seem to screw it up. I think it's exceptionally bad when AOPA project "giveaway" aircraft for example are offered up with such "bad" or invalid paint schemes too - but I have seen a lot of such paint schemes presented over the years.
Here is a list of Aircraft & N-numbers that I feel are not legal per the above requirements - if you care to look them up online and see some examples of which I "speak"...
Teal
N1322W see:
http://www.airport-data.com/aircraft/photo/000601627L.html
Aztec
N5329Y (font is wrong in terms of character size ratios and widths)
Twin Comanche
N7745Y (it's a wreck somewhere but the photo was online and the stripes within stripes effect was nasty!)
Aztec
N4695G (my photos date back to the '90's so it could have been repainted since...)
Twin Bo
N4373D (it's on the website of a Twin Bo "expert" in NY)
Aztec
N8075R (no contrast plus excessive "ornamentation")
Bonanza
N8140G (only contrast is outline which is not valid)
My list goes on....