Code:
awk 'FNR==NR {T[$1]=$2;next}
($1 in T) {$1=T[$1]}
1
' FS="=" file1 FS="," OFS="," file
clar_2400:3113[2323],,,[MIG_RLP_3113],40.000,[Pool 4],,,,,
clar_2400:3114[3333],,,[MIG_RLP_3114],40.000,[Pool 4],,,,,
clar_2400:261[2323],[if00p02wi],if00p02wi(4),[if00p_L],60.000,[Pool 0],,,,,
clar_2400:265[4444],[if00p02wi],if00p02wi(4),[if00p_L],65.000,[Pool 0],,,,,
clar_0986:208[5656],[recindc],rec-cj.hq.nt.newyorklife.com(4),[erec-cj_R1],950.000,[Pool1],BAU_erec,erec-208-1408-0996-2828,[erec1405_R2],clar_233:1408