There's more to experience when you log in!
EFAL is a Software Developer Kit that provides file format support for MapInfo TAB and MapInfo Enhanced TAB file formats. It supports opening, querying, editing and creation of new files. Querying of data is specified using the MapInfo SQL query language.
Looking at the docs, EFAL seems to have a set metadata function:
EFALFUNCTION void SetMetadata(EFALHANDLE hSession, EFALHANDLE hTable, const wchar_t * key, const wchar_t * value);
... which you could call after the initial create and having a valid session and table handle. The documentation doesn't, however, seem to list all the possible key values, which I presume includes blocksize. It might be as simple as "blocksize", or perhaps you can extract a list of possible keys from somewhere, or even write a small program to extract the data values from an existing table and see what secrets that reveals!