This simple scenario about different way to manipulation AS-path without prepend.

R1(AS100) — R2(AS200)

R1#
neighbor 1.1.2.2 remote 200

R2#
neighbor 1.1.1.1 remote 100
network 100.100.100.0 mask 255.255.255.0

AS-path prefix 100.100.100.0/24 from R1 is ‘200 i’
I will make AS-path from R1 is ‘500 200 i’

How to make it ? manipulate it with ‘local-as’

R1#
no neighbor 1.1.2.2 remote 200

Read original post at http://awanetwork.blogspot.com/2008/07/bgp-as-path-manipulation-without-as.html