Assalaamu alaykum. Please respond urgently. I guess that you know from my questions that I suffer from Waswasah (devilish/obsessive whisperings) in recitations. To make things easier for me, can I skip the first Tashahhud and limit myself to the following short version of Tashahhud in the final unit of prayer both in the individual prayer and in congregation? At-Tahiyyaatu lillaah; salaamun ʻalayka ayyuha An-Nabiyy; salaamun ʻala ibaadillaah as-saaliheen; ashhadu alla ilaaha illa Allah, wa anna Muhammadan Rasooluh.'” [Ar-Rawdhah]
Also do the rules of Tajweed (rules of recitation of the Quran) apply in the pronunciation of supplication/prayers that are outside of the Quran? For example, in the Tashahhud or Durood Ibrahim?

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 is His slave and Messenger. 

We advise you to say the Tashahhud while striving against your whispers; neither getting carried away with them nor giving any attention to them.

If Satan whispers to you that you made a mistake in pronouncing a given word, then just ignore his whispers and do not pay any attention to them.

The treatment is not in completely leaving the Tashahhud. The treatment is to repel the whispers and not pay any attention to them.

According to the view of the majority of the scholars, if you leave the first Tashahhud deliberately, your prayer is valid.

On the other hand, it is not permissible to observe the rules of Tajweed, such as the Ghunnah (which is a sound that comes out from the nasopharynx) and the like, in other than the Quran. For more benefit, please refer to fatwa 302365.

Allah knows best.