Change of rejected invoices to pending status in an unfinished payment cycle

This is not possible to do. If you reject an invoice and save it as such in either scheduled or invoice cycles, you can't bring it back into the incomplete cycle.
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When you reject and save an invoice, the system releases any payments that could link to it. This happens through purpose-built stored procedures that formally reject the invoice around the system when you ask them to (i.e., when you click Save).
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In an invoice cycle, once you reject an invoice, that invoice isn't available anymore. You'll need to enter a new invoice onto Mosaic for inclusion in another run of that cycle type. For a scheduled cycle, you'll need to run a new cycle to include the invoice again.