Well I've found that there is a possibility to edit the U-Boot Env with fw_printenv & fw_saveenv, but I don't know how. Maybe someone go experiences with this.

THX Destrukto

They are Linux application: sources are included in the UBoot distribution.
>./fw_printenv - Shows all the UBoot env parameters.
>./fw_printenv parm - Shows the parm env parameter.
>./fw_setenv parm value - Creates/Sets parm to value.