If I want to offer Salah Al-Haajah (prayer of need), can I make the intention of Salah At-Tawbah (prayer of repentance) as well?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is permissible for you to offer a two-Rakʻah (unit of prayer) prayer with the intention of offering Salaah Al-Haajah and Salaah At-Tawbah (prayer of repentance) together, because both prayers are not intended as independent prayers. Rather, they are fulfilled by just offering the prayer.

The Shaafiʻi scholar Al-Bujayrimi wrote, "The voluntary prayers that are not intended as independent prayers, such as the prayer of greeting the masjid, the Sunnah prayer after ablution, the Sunnah of Tawaaf (circumambulation), the Sunnah prayer upon assuming Ihraam (ritual state of consecration assumed for Hajj or ‘Umrah), the Ghaflah (heedlessness) prayer (between the Maghrib and the ʻIshaa’), the Istikhaarah (guidance-seeking) prayer, and the prayer of need..." [Haashiyat Al-Bujayrimi]

Haashiyat Ash-Shabraamallisi ʻala Nihaayat Al-Muhtaaj reads, "The Sunnah prayers whose intentions can be combined with other voluntary prayers are: the prayer of repentance, the two-Rakʻah prayer before execution, the two-Rakʻah prayer before consummating the marriage with the wife, and the like, because the objective is fulfilled by performing any given prayer."

Allah knows best.