UPDATE AVAILABLE! This minor update (v1.2.2) fixed a bug in the .ms script involving a wrong directory. THE 1.2.1 SOURCES ARE STILL VALID (=SAME) FOR 1.2.2.
This mod is a combination of a maxscript, an exe working in the background and a command line tool, all set-up to work together so that any Gmax user can from now on add, replace, delete, etc animations diretcly to an .ifp file from within Gmax without *any* extra work required.
The maxscript (which has been based on Kam's IFP IO script) writes all relevant data from Gmax to the Gmax listener window, the GTAMax tool (perhaps known to some readers from Kam's distributions) reads out the data and passes it all to the command line tool which handles the actual work of modifying .ifp files accordingly.
Relatedly, I have also recently released mod for VC that is called GTA:Martial Arts which allows as a side-benefit to fire any animation that is properly configured through it from the main.scm script at about any time. In conjunction with this distribution this should expand Vice City modding capabilities significantly. GTA:Martial Arts has been used for example in the production of that last PEDS episode of season 2 (Endgame).
For more details, see: http://www.gtaforums.com/index.php?showtopic=289154
I should add that this mod ist still in BETA status, so backup regularly.