Traya's assassins will eventually infiltrate and destroy the HK Factory on Telos, since the more security there is, the easier it will be to find, but that security can at best only delay the inevitable.
The HK factory had plenty of defenses, including various battle-droids, turrets, and mines. Not to mention that HK-50s will naturally be guarding the HK factory. Like, a lot of them.
We can see Traya's assassins fighting non-force users when they attacked the Mandalorain base on Dxun. They aren't super-advanced killer machines. The Mandalorians were able to hold them off, and undoubtably the HKs will be able to defeat them as well.
The HK factory won't be destroyed by assassins alone.
To get a glimpse of the HKs the assassins would have to go through, refer to this picture.