1 diplomat alone is probably not goig to be all that fun...
I had an ambassador with maxed out oratory skill, great bureaucracy skill, and I did that (while "trading" or during random RP events), and it took a long time to not yield much of a result. Really you'd want like 6 highly skilled ambassadors at the same time spread through the realm to have much of an impact. And their own diplomats and ambassadors can then come and undo your work for free, though.
I've been able to make some changes in a reasonable time frame.
To get a stronger effect and more interaction from the arrangement the realms ambassadors and diplomats could pair off and tour together. They can combine their skills to spread peace and while they're at it discuss which realm has been giving them funny looks.
