file modification over sshfs

I need you help!

I want to modify my configuration files on the beaglebone black over sshfs on my client pc
(The beagle is running debian over sd-card)

The filesystem of the BBB is already mounted on my client (ubuntu) pc with following command.

sshfs debian@beagle:/opt/ /mnt/beagle -o idmap=user -o uid=1000 -o gid=1000

I can browse through all folders but I can not change any file.
For example I changed to rights to following on the BBB:
-rwxrwxrwx 1 debian debian 16366 Dez 18 02:38 fhem.cfg

But I can not change it from the client pc?

Please help

For what it is worth, I have done something similar using the fish:// protocol in KDE. In the Dolphin file manager, I can point to fish://root@x.x.x.x, it asks me for a password, and from there I am good to go.