A bit of background: traditions and Tradition
When the Church refers to Sacred Tradition, she is referring, not to practices, but to a body of doctrines that are not explicitly found in the Sacred Scriptures.
A few examples of such doctrines (some of which rise even to the level of dogma, or solemnly defined doctrines that are subject to divine and Catholic faith):
The Immaculate Conception of the Blessed Virgin Mary. Although the Scriptures refer to Mary as kecharitomene (one who has been definitively filled with grace), it does not affirm in black and white that she was born without the effects of Original Sin.
The doctrine of Original Sin is itself an inference not found explicitly in the Scriptures.
The Assumption of the Blessed Virgin Mary. This event occurred, presumably, after most of the the New Testament was written, and so could not have been recorded in it (unless Revelation 12 is a veiled reference).
The canon of Scripture. The Bible does not itself contain a “table of contents;” which books actually belong to the Bible is a doctrine transmitted by Tradition.
The number of the Apostles. Nowhere in Scripture does it say that the office of Apostle is limited to the Twelve, or to the Twelve and St. Paul, or that the office would cease after the Apostolic Age. This is only known thanks to Tradition.
All of these are doctrines that have been taught, with differing degrees of explicitness, from the earliest moments of Church history. We can be sure that they are true, because of the infallibility that Christ endowed to his Church, and it is the task of the bishops in communion with the Bishop of Rome (the Pope) to be stewards and interpreters of these truths. In this capacity, they exercise the Church’s Magisterium, or teaching authority.
Sacred Tradition is to be distinguished from so-called ecclesial traditions (written with a lowercase T), which are various kinds of practices and popular beliefs that have developed over the ages.
Some of these practices are explicitly sanctioned by the Church (such as the various forms of the Sacred Liturgy), and others (such as novenas, rosaries, processions, and so on) are forms of popular piety, practices that people have found helpful for expressing their faith over the years.
Among ecclesial traditions are also certain popular beliefs that are not the subject of faith (many of which are probably historically spurious).
For example, the story of Veronica wiping the face of Christ, which is common in the Way of the Cross, has no basis either in the Scripture or in Sacred Tradition. There is nothing wrong with thinking that such a person really existed, but neither does the Church require such belief. Similarly, most depictions of the crêche show three Wise Men, but in fact the Scriptures do not specify their number.
No ecclesial tradition is completely set in stone (in contrast to Sacred Tradition), although, of course, ancient and venerable practices are generally to be respected. For example, even with the reforms of the Mass after Vatican II, the Roman Canon—now the First Eucharistic Prayer—was left essentially unchanged from the pre-Vatican-II Mass.
See the Catechism of the Catholic Church (CCC) numbers 80-90 for a full treatment of this topic.
How to judge if a practice is good and holy
There are objective ways to judge if a given practice is good and holy, or if, instead, it tends toward superstition.
- It should be in complete conformity with Church teaching (including, evidently, what is contained in Sacred Tradition).
- It should lead people to greater love and devotion to Jesus Christ.
- It should lead people to the Sacraments and to the reading of the Sacred Scriptures.
- It should foster obedience, humility, and the other virtues proper to Christian discipleship.
(These criteria are derived from the way that the Church judges Marian apparitions, which fall under the category of popular piety.)
Ultimately, it is for the Church’s Magisterium to decide whether a given practice, or even a popular belief, is helpful or not.
Regarding the specific concerns of the O.P.
It seems to me that a novena to Mary’s tears of blood is not a cause for concern. It is simply an example of popular piety.
No one is requiring Catholics either to believe that Mary shed tears of blood, or to take part in the novena. Both the popular belief and the popular practice are entirely optional. On the other hand, neither do they contradict any truth of the faith. If someone finds such a practice helpful, then he should feel free to participate. If not, then he is free not to do so.