Using awk
:
awk 'BEGIN{FS=OFS=","}{$NF=($NF>10?$NF+1:$NF)}1' file
$ cat file
449,615,43,57,8
308,617,43,57,3
345,558,43,57,11
$ awk 'BEGIN{FS=OFS=","}{$NF=($NF>10?$NF+1:$NF)}1' file
449,615,43,57,8
308,617,43,57,3
345,558,43,57,12
Can be reduced to as suggested by anubhava in comments:
$ awk 'BEGIN{FS=OFS=","} $NF>10{$NF++} 1' file
449,615,43,57,8
308,617,43,57,3
345,558,43,57,12