You can wear a scapular without an investiture, however a simple blessing is not an investiture.
The investiture is good in and of itself, even though you can wear the scapular without it, you should have it done when you can. It will help your devotion as well as give you the grace of the prayers involved in it.
To become a person who devoutly wears the scapular you should learn about its meaning and history, and
Carmelite spirituality.
*“Receive, my beloved son, this scapular of thy Order; it is the special sign of my favor, which I have obtained for thee and for thy children of Mount Carmel. He who dies clothed in this habit shall be preserved from eternal fire. It is the badge of salvation, a shield in time of danger, and a pledge of special peace and protection.” * Our Lady to St. Simon Stock
Those who put upon themselves the blessed scapular, clothe themselves with the uniform of Our Lady’s army, enroll under her banner, especially choose her for their Mother and Queen.
Or if you wear more than or a different scapular than the brown scapular, you are taking on the spirituality of the other religious orders that they are associated with. There are many small scapulars associated with various religious orders and ways of spiritual life.
The Carmelites wear their scapulars continuously both day and night, waking and sleeping, working and resting, living and to the day of their deaths. They are never taken off.
I think a person who wears the Carmelite scapular or brown scapular
should read St. John of the Cross or St. Teresa of Jesus’s writings, and read the scriptures about St. Elijah for example. Should consider pursuing the devotions associated with the Sabbatine privilege. Should be especially careful to observe chastity. Should be always thinking of Mary and her virtues, and pray some prayers devoted to her. And should especially observe the traditional fast days of the Church, rather than doing less than this.
‘Because all the forms of our love for the Blessed Virgin, all its various modes of expression cannot be equally pleasing to Her, and therefore do not assist us in the same degree to Heaven. I say without a moments hesitation that the brown scapular is the most favored of all!’
‘No devotion has been confirmed by more numerous authentic miracles than the Brown Scapular.’
St. Claude de la Colombiere
‘Perfection of life consists in drawing close to God. Heaven is the possession of God. In heaven God is contemplated, adored, loved. But to attain heaven it’s necessary to be detached from what is earthly. What is the life of a Carmelite if not one of contemplating, adoring and loving God incessantly? And she, by being desirous for that heaven, distances herself from the world and tries to detach herself as much as possible from everything earthly.’
St. Teresa of the Andes