In GlassFrog you cannot add/edit the Lead Links Accountabilities. 
The reason behind this is that a Circle’s Lead Link inherits the Purpose and any Accountabilities on the Circle itself, and controls any Domains defined on the Circle, just as if the Circle were only a Role and the Lead Link filled that Role. 

In practice the Lead Link's Accountabilities can be deferred to another role but in GlassFrog they will remain in the Lead Link's Accountabilities list.

For reference, here is Article 2.2.3 of the Holacracy Constitution: