I love this question. I think it’s natural to always be modifying your business model.
Recognize that if you choose to change things and leave your current customers in place (With their old price, or their old features) that you are kicking a can down the road. The best advice here is to give them a timeframe when you do this. For example, let’s say you raise your prices, but only on new customers. Even if it’s 5 years, you should tell your existing customers to expect an increase after x time. If you don’t, eventually, you will realize that having people on different plans starts to create product debt for you (and possibly technical debt). The support team always has to remember that their are old plans. Your financial reports have to remember this as well. It’s a long term tax on your business to have to carry these old plans forward, so setting a time limit is transparent and fair (even if customers want their price to stay the same forever).
Also, try not to make this mistake - charge a company a fixed price for unlimited use. The revenue you make should scale with the value given to the company (even if your $/user goes down as you make more money). Per user pricing does that. There are other methods as well. But one fixed fee is usually a mistake companies make early on that they have to undo later.
Also try to eventually get to a point where you have more than one pricing axis. If you have a SaaS business and you charge per user, then a company that has 10 people can only pay you so much until they add another employee. But if you have multiple plans (gold, silver, platinum - or standard, premium, enterprise) then you can upgrade that team to a higher plan (so two axis). Having more than two is even better but can make your billing start to get a wee bit complicated.