Sutra:
157. varththamAna nirththEsam Sathvam thalaiyeduththu anjinapOdhu anuSanthikkaikkAga.

Meaning:
The reason for using the present tense in saying "I am attaching myself to" (prapadhye) is to keep it in the mind when fear comes after the higher qualities (sattva guNa) arise in it.

Sri PBA Swami's Sarartha Deepikai:
Why is the present tense used here as opposed to using the past tense as in "nin adiyiNai adainthEn" and "adik kIzh amarndhu pugundhEn"?

The chetana living in this world will have rajas and tamas guNas initially and due to that would seek the wrong paths and the wrong goals. Later the sattva guNas would arise in him and he would then be afraid about his prior wrongful acts because the only counter-measure for those acts is surrendering to Him and that can be done only once.

Therefore, the present tense is used here to keep remembering that act of seeking His refuge.