I knew when I designed the Pleat Detail Dress and Top sewing pattern that I would be asked if it is possible to lengthen the sleeves....Yes it is and it’s not complicated, but it depends on the width of your fabric.
For instance the fabric I used here is 150 cm wide and this meant that with size M, the sleeve could be lengthened to a finished length of 55 cm from side neck. If the fabric were narrower a seam would need to be added at the centre front and back - its possible that this could add bulk in the pleat if the fabric was too thick.
To alter the sleeve length, continue the line of the sleeve, to the desired length and finish the new cuff length parallel to the original (A). I’m not sure how comfortable I would find the sleeves if they were much longer than just below the elbow, but there’s nothing to say it couldn’t be done. The fabric I used here is a medium weight linen, heavier than the lightweight denim shown in the pattern picture.
This fabric is less fluid and therefore the dress feels fuller to compensate I removed the inverted pleat from the back of the dress. To do this I folded back the pattern along the red line shown and then extended the stitch line from E to F right down to the hem (B). The dress is less full but is still possible to walk in.