Sometimes, if the interlock is listed for your exact panel catalog number and the interior has a place for a generator breaker that the kit can mechanically interlock with the main. A 100-amp main does not, by itself, forbid an interlock. It does mean the generator is backing up a modest service: you still have to size the inlet, the generator breaker, and the generator itself so you do not close every house load at once. Many 100-amp houses use a portable generator and a 30-amp inlet for essentials; that is a load-list question, not a kit-size question.
Compatibility is the usual constraint, not the 100-amp label. Kits are panel-specific. A fuse box, a Federal Pacific or Zinsco panel, or a can with no listed kit is the wrong place to improvise a sliding plate — see those safety pages and the backfeeding page. The electrician also has to keep working clearances and not bury the interlock behind a poorly planned generator breaker.
Size the generator with the generator calculator from a real load list (the fridge–furnace–lights example on this site is about 1,292 running watts and 2,300 starting watts using Honda’s figures plus a labeled lighting example). Never backfeed through a dryer outlet, and place the generator outdoors as the carbon-monoxide page describes.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.