What will happen if I chant the Bagalamukhi seed mantra "HLREEM" every day even when I have no deeksha given by any guru. Will it make any harm to me.
If your intentions in changing the mantra are pure and you call upon the grace of God and guru to assist and guide you, no harm will come to you from chanting the mantra. However, if you yourself believe that to do so without deeksha will cause harm then to go against your own belief will create an inner conflict and you should refrain from doing so.
I assume from your note that you have not taken deeksha from anyone? Perhaps you should consider or pray for guidance to a true teacher who can initiate you and give to you the guidance and spiritual blessings you seek.
In the meantime, you may pray to any great saint, master or diety to whom you have a natural devotion and deep respect that he/she may guide you in your spiritual practices.
But in all things be guided from within combining calm reason and calm feeling to do the right thing.