The amendments will, in the MoJ's words
"remove provision in the FPR and COPR which relates to powers, processes and orders under EU instruments or international agreements which will no longer be applicable or available when those instruments or agreements are revoked by the Withdrawal Act or the statutory instruments made under it, or in some cases amend such provision where such instruments are retained in an amended form."
The accompanying Explanatory Memorandum provides a useful review of the interconnection between UK rules and EU instruments, though clearly it is still a developing picture.
UPDATE: 11 March 2019
These regulations passed the sift requirements on 5th March. Read the SI as load before Parliament on legislation.gov.uk.