** Shares of Bentley Systems BSY.O up 5.9% at $55.42 before the bell as engineering software firm poised to join S&P MidCap 400 .IDX next week

** BSY to replace Western Union WU.N in the IDX effective before market open on Mon, Oct 6, S&P Dow Jones Indices said late Weds

** In turn, money-transfer service provider WU to replace Mr. Cooper Group COOP.O in S&P SmallCap 600 .SPCY

** Mortgage lender Rocket Companies RKT.N acquired Mr. Cooper in deal that closed on Weds

** S&P Dow Jones said Denver, Colorado-based WU's market cap is "more representative of the small-cap market space"

** WU shares, up 0.5% premarket at $8.12, had lost about 24% YTD through Weds

** Exton, Pennsylvania-based BSY has ~303.6 mln shares outstanding for roughly $16 bln market cap

** Through Weds, shares up 12% YTD

** Of 15 analysts covering BSY, recommendation breakdown is 9 "strong buy" or "buy", 5 "hold" and 1 "sell"; median PT is $61.50, according to LSEG

(Lance Tupper is a Reuters market analyst. The views expressed are his own)

((lance.tupper@tr.com ; 1-646-279-6380))