By Leika Kihara and Tetsushi Kajimoto TOKYO (Reuters) – The Bank of Japan has conducted a rate check in apparent preparation for currency intervention, the Nikkei website reported on Wednesday, citing unidentified sources, as policymakers stepped up warnings about sharp falls in the yen. Aside from verbal intervention, Japan has several options to stem excessive yen falls. Among them is to directly intervene in the currency market and buy up large amounts of yen. Below are details on how yen-buying intervention could work, the likelihood of this happening as well as challenges: WHEN DID JAPAN …