I would recommend NOT changing the K values at all. If you want to tweak EIGRP metrics, you can modify the delay on an interface. Changing bandwidth is also a possibility however if you are using QoS or monitoring software, that can throw many things out of sync and mess with your results/plans. Delay is a safe bet.
heheheh... Always be careful what you wish for. I had a client (against recommendation) who decided to change the K values to take load into account. While it may SOUND like a good idea because routes can change based on link utilization....
You always have to think about the impact on your routers too! how many routes? How often will values change? How much to you like your network freaking out?
I'd agree that you don't change it unless you need to. As you move into the CCIE lab studies, you'll "need" to because the lab will likely say so!
Yes, if we change the any k value other than default then EIGRP metrics get changed.
But, Cisco recommands to not to change the default values k1=1, k2=0, k3=1, k4=0, k5=0.
where k1 is bandwidth, k2 is load, k3 is delay, k4 is reliability and k5 is MTU.
Load on a link depend on the traffic on that link and as the traffic increases/decreases, value of load changes and if you are using k2=1, then metrics also changes with traffic load.
Reliability of a link also varies between 0 to 255 depends on errors on link and end user device`s capabilty.
MTU depends on the technology standards means on fibre links MTU is different then 802.3. so if there are differrent media are used in a network then it can be a problem.
Rest of the two are predefined and not changes automatically.
You are right in yout thoughts. EIGRP will take reference of calculations that you globally specify with the "metric weight" command (in protocol config mode) or per route basis using route-maps and setting the routes with the metric that you will inside the route-map. Awesome stuff!