Since 2018, the BESSY II storage ring has operated a cryogenic permanent magnet undulator (CPMU), which was developed and constructed in-house. With a period of 17 mm, CPMU17 was the first in-vacuum undulator to be installed at BESSY II. Another CPMU (CPMU20) and the world’s first in-vacuum APPLE II undulator (IVUE32) are currently under construction and will be installed at BESSY II within the next few years. To meet the needs of its diverse and ever-evolving user community, BESSY II has pioneered innovative operating modes, such as low-alpha and TRIBS, in addition to the hybrid mode. These special operating modes are based on phase space manipulation, which is enabled by the accelerator lattice's great flexibility and tight tolerances for the insertion devices. Accordingly, there are also tight tolerances on in-vacuum IDs. This paper discusses some of the main challenges, as well as the key developments and strategies, involved in meeting tolerance requirements.