Innovation is divided in two types:
1. Innovation that reaches the level of kufr (Bid'ah mukaffarah): Like the innovation of stating that the Qur'aan in created, and cursing the Sahaabah such as Abu Bakr and 'Umar and casting aspersions upon the wives of the Prophet (salallaahu 'alaihi wasallaam) and in specific A'isha (radi Allaahu 'anhaa), the one who was freed [from false accusations] from above the Seven Heavens - So as for these [types of] people, then it is not permissible to invoke Allaah's Mercy for them.
2. However, we do invoke the Mercy of Allaah for the people of bid'ah whose innovation does not reach the level of kufr (mufassaqah) - that which does not reach the level of kufr in action or 'aqeedah (belief).
(1) i.e. to say "rahimahullaah".