Renaming

Add a tag before the suffix:

for i in *; do mv -v "$i" ${i%.*}-tag.suffix; done

file12345.suffix will become file12345-tag.suffix.

Remove a tag before the suffix:

for i in *; do mv -v "$i" ${i%-*}.suffix; done

file12345-tag.suffix will become file12345.suffix.

Add ascending numbers:

for i in *; do ((num++)); mv "$i" $(printf "%03d%s" $num)-"$i"; done

file.a.suffix will become 001-file.a.suffix, file.b.suffix will become 002-file.b.suffix.

Cut off leading numbers:

for i in *; do mv -v $i $(echo $i|cut -d'-' -f3-); done

001-file.a.suffix will become file.a.suffix again, 002-file.b.suffix will become file.b.suffix.

In case the numbers were added at filename’s end like file.a-001.suffix

for i in *; do mv $i $(echo ${i%.*}|rev|cut -d'.' -f2-|rev).suffix; done

file.a-001.suffix will become file.a.suffix again, file.b-002.suffix will become file.b.suffix.