Certain Btrees are indirectly created and managed by WT, and they should not be (easily) modified using the API and/or wt utility.  For example, .bf files (bloom filters created by LSM) and .wti files (index files) can be created.  Once that is done, wt dump and/or  wt load can be invoked to view and/or modify the contents of the file, or opening a cursor on these files in a program to modify them.  These files can also be dropped.

We might consider ways to prevent direct modifications, at least, of these files.  Some files like WiredTiger.wt appear to already be protected in this way.