[Mauzen]

Thats how id do it without testing or deeper thinking

pawn Код:

new pos = strfind(string, "д", false, 0);
while (pos > -1) {
    string[pos] = 'a';
    strins(string, "e", pos+1);
    pos = strfind(string, "д", false, pos-1);
}

Maybe pos+1 in strins needs to be just pos, the rest should work