When it comes to managing change then what ever practices you decide to adopt, its preferable to take an "all in" approach, in that you get as many people involved as you can. This does not mean that you have to adopt everything all at once, but helps you understand the big picture of change within your organisation.
An all in approach gets people involved from all aspects of the business (including revenue generating customers), so you understand the most important issues surrounding change within the business.
An all in approach helps you set meaningful goals that support the business value (e.g. your customers) and aim to extend that business value (e.g.. more customers, happier customers)
For example, if you make a decision that scrum has benefits for your organisation, it is better to get more people on board with adopting the idea of scrum than it is to adopt a full blown implementation of a scrum based process for a select few.
Although scrum is a framework, to get the most out of scrum you need to implement that framework in a way that increases the agility and effectiveness of whole company. It is too challenging to go from nothing to a full blown scrum process in one day (or one sprint) as this would be too much change for most companies (unless you are already agile in all but name).
Adopting XP practices also take time to bed in, whilst most of these practices are pretty straight forward and easy to get going, they take a little longer to become natural and comfortable. Adoption will be much smoother if there is an all in approach where everyone can see the point of these new practices (overal goals and values)
Adopting Kanban is relatively low impact at first as you are not trying to introduce change into your practices, you are simply trying to visualise and expose the relevant details of your current working practice. Using a Kanban method approach to represent everything thats valuable with your practices in a way that is engaging to work with and highly representative takes time and should continue to evolve as your practices evolve.