It is not just data we need to think about - but also the file system and the metadata associated with the files as well as the file system.
If ( a big IF ) we can determine for sure that BitLocker has only encrypted the free space so far (skipping all else), then the question you asked becomes at least a theoretical possibility (still depends on how BitLocker code is written - whether it detects changes to disk after it starts encryption, and how it handles such changes).
In general, file system data is not only stored at the beginning but also some redundant copies are stored in other places.
We must assume that BitLocker has already encrypted such metadata - and any changes you make to the file system (such as deleting files) changes the already encrypted data (including free blocks, number of files, directories, etc).
So my answer is NO. You're much better off stopping the encryption altogether; doing whatever housekeeping you want to do and then restarting afresh.