Can Astrological remedies nullify the malefic effects of the planets ?

No remedies can nullify the malefic effects of any planet. In my years of experience in consulting astrology I never found that a remedies given to the person had nullify the malefic effects of the planets. No doubt it will definitely decrease the negativity of its malefic effects. The decrease of the effect can't be quantified. It will differ from person to person.

In today's astrology the remedies that are in practice are :
Mantra Shastra : A vedic mantra ( a group of words ) is asked to enchant for a stipulated number of times. The vibrations generated by the mantra will act to decrease the malefic effects of the planets. But it only works when one follow the strict instructions of the rules and the system.

Yantra Shastra : A geometrical design or some text writing is inscribed on some metal ( generally copper ) or Bhoj patra ( bark of the tree Betula Utillis found mostly in the forest and Himalayan region ). It has to be written with the pen made of the branches of the particular tree only. The ink has to be made by crushing particular leave and or some roots of plants or and trees. Again the parameters for making Yantra is tough not difficult and in today's day for common people its tough to do. After making Yantra, its puja is done to minimize the negative effect.

Ratna Shasta : A gems is in form of ring or locket is given to worn. The gem of the particular planet catches the vibrations of that planet and impart them to our body. This in turn minimize the negative effect of the malefic planet. There are system prescribed for ring wearing according to shastra. Its easy and can be done by common people. Duplicate ratna or look alike ratna will not give result, on the contrary it will give negative result as the vibrations of the particular planet coming thru the real ratna ( gems stone ) is due to its refractive index of that stone.

Totka : This kind of remedies are in lakhs and vary from region to region. This is a easy practice that can be performed by common people. The effectiveness of its depended on the person’s faith and believe on it. As there are lakhs of totka so you can't say which one is real and which is fake. 

As these all are not imparted by well know people and neither there are big granths specially devoted to this knowledge. Today fake remedies seller design such totka according to the person and make the quite attractive and catchy to make money out of it Because you have no tool to judge its authencity.

Now for a remedy seeker it all depends on his decision which he finds to be easy and can be done with full devotion.