Your 90-day limit applies to any 180-day period, not to the entire 5-year period of the visa's validity. The maximum number of days you could spend in the Schengen area, therefore, is slightly more than 900. You must be careful to adhere to the 90/180 rule, though. There are several questions related to that on this site, including How does the Schengen 90/180 rule work?.
Oddly, the EU's public information pages on Schengen visas don't make this very clear. The Schengen Visa Code, however, is more explicit, in Annex VII (Filling in the visa sticker), section 4:
- ‘DURATION OF VISIT ... DAYS’ heading:
This heading indicates the number of days during which the visa holder may stay in the territory for which the visa is valid. This stay may be continuous or, depending on the number of days authorised, spread over several periods between the dates mentioned under 2, bearing in mind the number of entries authorised under 3.
The number of days authorised is written in the blank space between ‘DURATION OF VISIT’ and ‘DAYS’, in the form of two digits, the first of which is a zero if the number of days is less than 10.
The maximum number of days that may be entered under this heading is 90.
When a visa is valid for more than six months, the duration of stays is 90 days in every six-month period.
I suspect that this information makes your original questions irrelevant, but for the sake of being thorough, here are the answers:
If you exceed the allowed stay under the 90/180 rule, your visa will probably be revoked or annulled.
If you have a legitimate reason for spending more than 90 days in a given 180-day period, you may be able to apply for a national ("type D") visa from the country where you will be spending the bulk of your time. Requirements for these visas vary, however, because they are controlled by national law. In practice, it is almost certainly easier to spread your travel out so it complies with the 90/180 rule.