# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(?:\([^),]*|\G(?!^))\K,([^),]*)/+$1/g;t' <<< "Lorem ipsum dolor sit amet, consetetur sadipscing (elitr, sed diam nonumy eirmod tempor invidunt, ut labore, et dolore magna aliquyam erat), (sed diam) voluptua. (At, vero) eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet."
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html