regtrans-ms files that were created prior to the last system boot can be safely deleted. There's no way they will (or should) be written to the registry, so they're junk.

What is regtrans-ms files?

REGTRANS-MS files are created with the Microsoft Common Log File System, a Windows component used to create transaction logs. They contain transactions, and read and write information about changes to the user or system registry restore data, which is stored in the NTUSER. DAT or SCHEMA.

What is BLF?

BLF is a log file created by the Common Log File System, a Microsoft Windows component used for creating transaction log. It; contains metadata that is used to manage access to the log dat, and; can be created using the CLFS (API). It is used with containers which are associated files that hold the log data.