Ah… it's not that TTL that you need to change. The command you are using modifies the maximum TTL.
When you change the max-hop limit, during packet delivery this value is embedded in the packet as well, hence regardless of what you set the ISP only needs to check if the TTL is,“max - (value >=2)".
What you need is to ensure, your TTL when reaching carrier device is ( max - 1).