Nein, der modifizierte Bibliothekscode darf nicht closed-source sein. Siehe Sektion 4:
You may copy and distribute the Library (or a portion or derivative of it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above
provided that you accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange.
If distribution of object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place satisfies the requirement to distribute the source code, even though third parties are not compelled to copy the source along with the object code.
Ach ja, da hätten wir noch einen Punkt, steph-7. Du musst auf der Webseite des Programms ebenfalls den Source-Code der Library zur Verfügung stellen.