I don't know what Marweld is, it sounds like a trade name for a product. Maraging steels are a class of high strength steels quite a bit different in composition from H13 with a completely different mechanism for developing strength and hardness. While hardened Maraging  (C) 300 has properties similar to hardened H13 and might be used for the same purpose, I [not knowing for sure that it can be done] wouldn't suggest using a Maraging filler on the H13 due to the area of dilution between the 2 being some unknown mixture with unknown properties. The Maraging literature says that IT [maraging steel] can be welded without preheat, so I guess it can. Conventional tool steels are preheated to reduce the chances of cracking from streses from the weld deposit contracting as it cools. I tried to google "Marweld" and couldn't get anything usefull, I did come up with Eureka electrodes in My search, but it is not the same Eureka that made the tool & die electrodes years ago. If anybody has a definative answer, I too would like to read it.