Wearing tilak, doing deva pooja etc on Sraddham day..

 Wearing tilak, doing deva pooja etc on Sraddham day..

you asked about wearing tilak or vibhooti before tarpanam..

The rules are formed from similar situations for Sradhams.. because what you mean by Tarpanam even on amavasya or sankramanam is just a sraadham...

The rules as seen in the text SraddaKalapalatha.. quoting other sages is reproduced below.

वामहस्ते तु दर्भांश्च गृहे रङ्गवलिं यथा

ललाटे तिलकं दृष्त्वा निराशाः पितरो गताः॥

श्राद्धसङ्ग्रहे

ऊर्ध्वं पुण्ड्रं द्विजातीनामग्निहोत्रसमो विधिः।

श्राद्धकालेऽनुसंप्राप्ते कर्ता भोक्ता च तत् त्यजेत्॥

तिर्यक् पूण्ड्रम् यथा दृष्ट्वा स्कन्धे माल्यान्तथैव च

निराशाः पितरो यान्ति दृष्ट्वा च वृषलीपथिम्॥

प्राक् पिण्डदानाद्गन्धाध्यैनाऽलङ्कुर्यात्स्वविग्रहं

दानाऽध्ययनदेवार्चाजपहोमव्रतादिकान्

न कुर्याच्छ्राद्धदिवसे प्राग्विप्राणां विसर्जनात्

श्राद्धकल्पलतायाम्॥

vāmahaste tu darbhāṁśca gṛhe raṅgavaliṁ yathā

lalāṭe tilakaṁ dṛṣtvā nirāśāḥ pitaro gatāḥ||

śrāddhasaṅgrahe

ūrdhvaṁ puṇḍraṁ dvijātīnāmagnihotrasamo vidhiḥ|

śrāddhakāle'nusaṁprāpte kartā bhoktā ca tat tyajet||

tiryak pūṇḍram yathā dṛṣṭvā skandhe mālyāntathaiva ca

nirāśāḥ pitaro yānti dṛṣṭvā ca vṛṣalīpathim||

prāk piṇḍadānādgandhādhyainā'laṅkuryātsvavigrahaṁ

dānā'dhyayanadevārcājapahomavratādikān

na kuryācchrāddhadivase prāgviprāṇāṁ visarjanāt

śrāddhakalpalatāyām||

In sraddha sangraha it is said

When pitrus visit us for receiving Shraddham and find us holding darbha in the left hand, seeing rangoli in the home, finding tilakams on our forehead, return in desperation (without receiving Sraddham)

Wearing Oordvapundra for brahmins is equal to doing agnihotram.. But when the Sradham arrives the person who is doing the Sradham and the persons who partake in the ceremonial feast should give up Oordhvapundram

Seeing oordhvapundram or horizonal lines on the forehead,and seeing garlands around the neck of the one who perfoms Sradham, and finding the performer as the husband of a woman in impurity, the Pitrus return in despair.

Before pindapradhaanam on the sraddham day, the performer should not decorate himself with Sandal paste and other decorating materials

On the Sraddham day, before the Pitrus..or the brahmins on whom pitrus are invoked, are released or ceremonially sent away after meals, making gifts, learning vedas, doing pooja and archana to Devas, doing japam, homam etc are prohibited.