I have added a function to edit/add Header / License text metadata in the sche/sym files. Properties -> Edit Header/License text (Shift-B). Any text written there will be visible at the very beginning of the sch/sym file:

v {xschem version=3.1.0 file_version=1.2
* Copyright 2021 Stefan Frederik Schippers
* 
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*     <https://www.apache.org/licenses/LICENSE-2.0>
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.

}
G {}
K {}
...
...

The above text of course can also be added manually by editing the text file and inserting directly the text after the first version line and before the closing '`}`' bracket. Any

{

or

}

or

\

characters in the text must be escaped (like

\{

).