In principle you should build a website so that all text and images, maybe a logo and buttons for submitting a form etc excepted, can be modified by the web authors. If you don't have this, you will rely on the developers to make content modifications to the website. This is far from ideal because this is very costly, requires planning and when you have urgent cases at hand it will just lead to stress between the business and technology team.
Unfortunately this ideal situation requires that you architect the site accordingly and accept the extra effort, time and costs upfront. When you are aware of these issues, you can plan this in but you need to look whether these upfront costs are warranted. If the website is expected to have a limited life span and during this time only certian sections of the site require updates, you can consider to leave the other parts as static HTML or hard coded in software. It will only become a problem if the website will live longer than originally planned or if more sections of the site need to be updated than as originally planned.
When you have outsourced the development, support and maintenance to a vendor, you will not have good insight how they will have built the website. If the vendor also is responsible for making the content changes, you will only see how they have resolved it once you take over the support and maintenance in-house. This can be a shocking experience.
The way around this is to QA the vendor's work regularly, not just at the end or when you get the handover. You can put clauses in the contract but it is far from ideal to involve lawyers when it has gone wrong. And it will. Involving lawyers and going to court will only be a lose-lose result. So you either you need to accept extra upfront costs or accept the risk. And since money is a scarce resource ...
