The flip-flop operator can help:

use strict;
use warnings;
while(<DATA>){
    next if m|^/\*.*\*/|;
    print if /^OT;$/../^RT;$/;
}

__DATA__
OT;
some line
/*asas*/        ##here comments should be removed
/*asdas*/  #OT;.....RT;should be replaced with OT;.....DT;OT.......RT;
some line
RT;

some lines 
somlelines

OT;
some line
/*asas*/
/*asdas*/
some line
RT;
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