Move 'carrying a pale yellow backpack with a flower charm' earlier in the prompt, right after the subject description, and add 'close-up on backpack detail' or 'three-quarter turn showing backpack' to the camera field instead of 'centered front-facing view, full-body shot'. You could also add 'oversized backpack' to exaggerate its scale relative to the character.

Swap 'soft studio lighting' for 'dramatic rim lighting with deep shadows' and change 'plain neutral cream background' to something like 'dark charcoal background with subtle fog'. You'd also want to drop 'cheerful and whimsical design' in favor of a phrase like 'melancholic and quiet design' to pull the character's expression away from the current blush and bright-eyed look.

Keep 'smooth clay-like toy figurine style, cinema 4d render' and 'soft pastel color palette' fixed since those anchor the render quality and color mood, then just swap the clothing list, 'periwinkle sweater over a white undershirt, denim overalls, purple leg warmers, and purple Mary Jane shoes' for other combos like a mint raincoat and yellow boots, or a coral cardigan and white sneakers. Changing only the wardrobe phrase while leaving lighting, camera, and background language untouched will keep the series visually consistent.