Running Nokia 5110 with 3 pins
What you want to do (one falling edge on SCE, keep it low ever after) is allowed according to the PCF8544 datasheet, but it has a lurking problem: you no longer use the SCE edges to indicate the byte boundaries, so after one clock missed (for example due to noise), you will be forever out of sync with the LCD.

An IMO better approach would be to use a SPI extender (a simple HC595 will do) to supply all the signals in your system that need to change only rarely (for the LCD: res). This approach takes the same number of pins as driving all LCD pins directly, but gives you 7 'slow pins'.