All these shapes can be represented with Sinhala Unicode. Similar to modified consonants such as "ku", they are created using sequences. These sequences include the Zero Width Joiner (ZWJ), a shared character in Unicode to form joint letters / ligatures.
Examples:
Rakaransaya and Yansaya represents "al kireema" + "rayanna" and "al kireema" + "yayanna" respectively as a mandatory ligature, while Repaya represents "rayanna" + "al kireema" as an optional ligature.
Please note that the end user doesn't need to know anything about ZWJ and other technicalities. Keyboard drivers generate proper sequences. For example, my Sayura keyboard scheme uses the key R for rakaransaya, and pressing that generates "al kireeka" + ZWJ + "ra" sequence. Dushara's Wijesekara keyboard driver also does the same.