Insert text with Sed (in various positions)

Hello. I'm trying to insert text in various positions and I could only do that using pipes for each position.

Example:

cat file | sed -e 's#\(.\{5\}\)\(.*\)#\1:\2#g' | sed -e 's#\(.\{26\}\)\(.*\)#\1:\2#g'

Insert ":" at position 5 and 26.

it can be done in the same sentence, without using pipes?

Help please. Thanks.

sed -e 's#\(.\{5\}\)\(.\{20\}\)\(.*\)#\1:\2:\3#g'  file

thanks!

 awk -vFS= '{$5=$5".";$26=$26"."}1' OFS= file 

sed 's/./:&/26;s/./:&/5' file