The Collaborative International Dictionary of English v.0.48:

Modify \Mod"i*fy\, v. t. [imp. & p. p. Modified; p. pr. & vb.
   n. Modifying.] [F. modifier, L. modificare, modificari;
   modus limit + -ficare (in comp.) to make. See Mode, and
   -fy.]
   1. To change somewhat the form or qualities of; to change a
      part of something while leaving most parts unchanged; to
      alter somewhat; as, to modify a contrivance adapted to
      some mechanical purpose; to modify the terms of a
      contract.
      [1913 Webster]

   2. To limit or reduce in extent or degree; to moderate; to
      qualify; to lower.
      [1913 Webster]

            Of his grace
            He modifies his first severe decree.  --Dryden.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "modifying":
   altering, assuasive, bounding, extenuating, extenuatory, lenitive,
   limitative, limiting, mitigating, mitigative, mitigatory,
   modificatory, modulatory, palliative, qualificative, qualificatory,
   qualifying, restricting, restrictive, softening