With this ficus I will really need a lot of research before I try it. And it will be major.
Key to rootbal reduction are 3 things:
- Timing (The plant should be at the start-to middle of the optimal growing season to allow for speady recovery
- Selective trimming: Ideally you have only very few cuts, that take out the biggest roots. Smaller roots you leave. Try to cut bigger roots at a point of branching, leaving a side-root with actively growing (white-tipped) roots
- Aftercare: The plant should not directly be exposed to drying winds, hot sun etcetc.
Optional item 4: If you expect to reduce the rootbal a lot, you could a few days beforehand already reduce the foliage mass. Doing this a few days beforehand will give the plant some time to start seasling the worst damage (seasling the wound from losses of water). Reducing the foliage will put less of a strain on the roots after repotting.
I normally do this only by out-of season repotting, and/or layers.