From the German song "Mein Herz brennt",
The lyrics everywhere online have this
Sie kommen zu euch in der Nacht
Und stehlen eure kleinen heißen Tränen
Sie warten bis der Mond erwacht
Und drücken sie in meine kalten Venen Rammstein: Mein Herz brennt
Here I think "meine kalten Venen" should be in the accusative case, and hence the adjective "kalten" should be changed to "kalte", am I right?
You are facing the problem of differentiating between strong, weak, and mixed declension of adjectives. I will illustrate the three forms with the adjective kalt and the plural noun Venen in accusative case.
The form kalte, which you think was correct, is called strong declension. It appears when there is no article or other word declined like an adjective:
kalte Venen
In your example, however, the strong declension does not work, because the pronoun meine is also declined like an adjective.
The weak declension appears in connection with a definite article:
die kalten Venen
Finally, when there is yet another adjective, or a word that is declined like an adjective (such as meine), then mixed declension is used:
meine kalten Venen
This is actually the form in your example.
The sentence is correct, but's in fact a bit tricky.
Because the possessive "meine" acts as a kind of article and, having an ending, carries information about case and number, the following adjective is weak.
Let's look at the simple cases:
In kalte Venen
Strong adjective because there is no article.
In die kalten Venen
Weak adjective because of the definite article.
In meine kalten Venen
Also weak because, as I wrote above, the possessive has an ending with information about case and number.
On the other hand, it's:
Mein rotes Auto
Because "Mein" does not have an ending and does not carry information about case and number, the following adjective has to be strong.
Here is the full paradigm with "meine kalten Venen" (a somewhat strange topic for a song, though), both with mixed and strong declension endings (for explanation of this difference see other answers on this page):
Wer? - Meine kalten Venen sind gut sichtbar. - Kalte Venen sind gut sichtbar.
Wessen? - Meiner kalten Venen Blut steht still. - Kalter Venen Blut steht still.
Wem? - Meinen kalten Venen täte jetzt ein Schnaps gut. - Kalten Venen täte jetzt ein Schnaps gut.
Wen? - Meine kalten Venen rubbele ich so lange, bis sie wieder warm werden. - Kalte Venen rubbele ich so lange, bis sie wieder warm werden.
The same thing in singular:
Wer? - Meine kalte Vene ist gut sichtbar. - Kalte Vene ist gut sichtbar.
Wessen? - Meiner kalten Vene Blut steht still. - Kalter Vene Blut steht still.
Wem? - Meiner kalten Vene täte jetzt ein Schnaps gut. - Kalter Vene täte jetzt ein Schnaps gut.
Wen? - Meine kalte Vene rubbele ich so lange, bis sie wieder warm wird. - Kalte Vene rubbele ich so lange, bis sie wieder warm wird.
(I am glad that I do not have to learn German... what an annoying language!)
I struggle, however, a bit with finding a realistic context for "und drücken sie in meine kalten Venen". Perhaps
Komm, wir kaufen zwei-drei Spritzen Heroin und drücken sie in meine kalten Venen.
This would be socially reprimandable and health-wise unwise, but grammatically it is completely okay.
Or is this about something happening inside (location! Dative!) the veines, as opposed to towards (direction! Accusative!) the veines? A dative construct would require a slightly more complex sentence:
Ich habe mir in Brasilien Drachenwürmer eingefangen. Nicht nur zwicken und drücken sie in meinen kalten Venen, man sieht sie auch noch durch, und das findet meine Freundin unschön.
It is accusative case (mixed inflection because of "meine"), but it's plural. "Kalte" would be singular, but "Venen" is plural, so only "kalten" fits.
