If I were to change my weights, does that only affect the eigrp neighbors, or do all my upstream routers need to be changed as well?
If I have:
R1 (connected to R2 and R3)
R2 (connected to R5)
R3 (connected to R6)
I change my delay on R1, would I need to change the metric on ALL of the routers? Since it goes under the process, I would think it would affect all of the routers, which in my mind is a bad thing. Why would I ever want to change delay instead of letting the protocol figure it out?
I'm not sure what the delay is between these links by default (let's say 1000 for ease of math). So, I would change the k-value for delay on R1, R2, and R3 to keep the adjacencies up. Does that mean that all of my delay has been changed by three for each hop?
R1 (1000*3=3000) --> R2 (1000*3=3000) --R3 (1000*3=3000)?
Yes, but the composite metric will be shown under the EIGRP route based on the formula I posted before. The delay modification will alter the EIGRP composite metric value but the idea you've presented is technically correct.
Also, what happens if I have two interfaces on R1, and I don't want the k-value to be modified for the other router. R1 is connected to R4 also, but I want the delay to be 2 instead of 3. Is that possible?
No, it affects the whole EIGRP process, it's not a per interface modification.
As I stated before, for per-interface modification, simply use the delay command under the interface without altering the metric weights.
for per interface manipulation you just need to do what Edison suggested:
verify current delay with
sh int type x/y
int type x/y
this doesn't change the K-values
Hope to help